Here are some very common errors made by beginners who seem clueless when it comes to the proper way to gain strength and  muscle mass:

• Overtraining

     More is not necessarily better when it comes to weight training in the gym.  Your body needs time to recover when it's put under the stress of heavy lifting.  Remember, when you perform weight training exercises you are literally tearing down muscle fibers.  This means that in order for your muscles to grow the muscle fibers must undergo a healing process.  If you fail to allow adequate recovery by giving at least 48 hours rest before hitting the same muscle group, you will likely fail to gain any appreciable muscle mass.  Weight training provides the stimulus for growth but rest and proper nutrition is what's needed for the growth process to occur.    Bottom line:  Train each bodypart hard 30 to 60 minutes per session once per week and do cardio 20 to 30 minutes per session 2 to 3 days per week.

• Ego lifting

     In order to gain strength and muscle mass, you must lift progressively heavier weights over time.  In other words, patience and discipline is required to make quality gains.  Piling on a ridiculous amount of weight to gain strength and muscle mass faster is foolhardy at best and injurious at worst.  Using bad form, bouncing the weight, and performing very short range of motion while straining to lift enormous amounts of weight is a recipe for disaster (read:  injury).   Bottom line:  Utilize small incremental increases in weight from workout to workout while performing lifts.   

• Avoiding failure

     Failure in weight training is a good thing.  This means that you are lifting a weight as many repetitions as possible until you're not able to perform one more rep.  Soreness is the name of the game when lifting to failure.  Just going through the motions is not going to cut the mustard.  The weight lifted must be challenging enough that if your goal is to perform 10 reps, you will need to utilize intestinal fortitude in order to perform 11 reps.  Each and every set needs to be this challenging in order to warrant a rest period.  Be sure to limit any intensity technique such as drop sets, forces reps, rest-pause, etc. for the last set of an exercise in order to lessen the risk of overtraining.  Bottom line:  Make each and every set count by lifting a weight that causes muscle fatigue. 

• Avoiding leg training

     If you're not training legs as intensely as arms, you are making a big mistake when it comes to gaining overall strength and muscle mass.  Legs consist of the largest muscles within the body.  Why would you want to avoid training such large muscles unless you'd prefer to have an imbalanced physique (i.e., humongous arms sidelined by toothpick legs!).   If you want to get big, you need to squat, period.  Compound movements such as squats, leg presses, hack squats, and lunges is what's needed to build a respectable physique.  The bonus is training legs spurs more growth hormone release than training the upper body.  Not only this, but your metabolic rate will increase significantly as well due to the increase of quad, hamstring and gluteal muscle mass.  This means more calories will be burned while resting.  Not a bad tradeoff.  Bottom line:  You must train legs if you want to gain appreciable strength and muscle mass.

    There are principles of training you should abide by in order to gain muscle mass.  Here they are:

• Overload Principle

    Since your body adapts to the stimuli placed upon it, you should continually increase the intensity (i.e., loading) of exercises to get stronger and therefore gain muscle mass.  Incremental changes must occur (i.e., increasing the loadings, reps, or sets) to keep the body guessing and stimulate further muscular growth.

• Periodization Principle

    This principle essentially entails splitting your training into what are called mesocycles (e.g., endurance, mass, strength, power), each of duration from about one to three months.  The purpose here is to focus on a particular resistance training goal (e.g., gain muscle mass) which falls within one mesocycle.  Recommended training programs incorporating certain techniques (i.e., compound sets, supersets) and parameters (i.e., %1-RM, number of sets, number of reps, rest periods) are then employed in an effort to achieve the resistance training goal.    

• Nutrition Principle

    If you want to gain muscle mass, for example, you need to eat BIG.  That is, strive to eat a lot of clean food to feed your muscles.  You must maintain a positive caloric balance, meaning you're eating more calories than you are expending during each day.  Your recommended caloric intake is essentially based on five parameters:  bodyweight; height; age; lean body mass; and physical activity level.  Once you've determined how much you should eat, you need to break the macronutrients down into percentages of caloric intake (e.g., to gain muscle mass, eat about 65% carbs, 25% protein, and 10% fat).  Now split up you caloric intake into six to eight meals per day.

• Sleep Principle

    If you want to get big, plan on getting at least seven hours of sleep daily.  Why?  Because adequate sleep is necessary to allow for enough growth hormone release and muscle recovery from hard training to take place.    Growth hormone enables the muscles to grow and facilitates joint repair and fat loss.   Most importantly, adequate sleep is needed to replenish your energy levels to push heavy weights and train intensely.  

• Supplement Principle

    Remember, nutritional supplements are designed to supplement your diet, not to take the place of it.  Determine all the healthy, clean foods you should be eating first before incorporating certain supplements into your nutritional regimen.  Here are the must-have supplements for gaining muscle mass:  

1. Whey protein--take before breakfast, pre- and post-training
2. Creatine monohydrate--take pre-and post-training
3. Multivitamin--take with breakfast
4. Fish oil--take with breakfast
5. Glutamine--take with whey protein and creatine
6. Branched-chain amino acids--take with whey protein and creatine
7. Casein protein --take before bedtime and post-training
   

• Confusion Principle

    This principle entails applying varying training techniques (e.g., supersets, drop sets, rearranging exercise order, etc.) to keep your body guessing in order for it to continually adapt and therefore grow.

• Repetition Principle

    If you want to gain muscle mass, you need to keep your repetition range within the so-called hypertrophy range:  eight to twelve reps.  

• KISS Principle

    It's all about Keeping It Simple, Stupid!  Don't make your training more complicated than it needs to be--stick with the basics:  use free weights for compound movements (e.g., bench press, squat, deadlift) and avoid balance platforms, stability balls, etc.  
 

    If you want to get the most bang for your buck, stick with mostly free weight, compound (multi-joint) movements in order to efficiently gain muscle mass.  
    Here are the best exercises you can do (in no particular order)  for your muscles in the gym to develop and gain quality mass on your frame:

• Barbell Curls   (biceps)
• Dumbbell Bench Press   (pecs)
• Dumbbell Overhead Press   (delts)
• Dips   (triceps)
• Barbell Front Squats   (quads)
• Stiff-Leg Barbell Deadlifts   (hams)
• Standing Calf Raises   (gastrocs)
• Wide-Grip Long Bar Pulldowns   (lats)
• Crunches    (abs)
• Lunges   (glutes)
• Forearms  (wrist roller)

    The best overall muscle-building and fat-burning exercise ever:

• Barbell Back Squats  (innervates the most muscles of the body and stimulates the most growth hormone release)

    The answer is yes, it is okay to cheat or use "body english" when lifting weights.  Cheating involves incorporating assistive or ancillary muscles in order to facilitate the execution of a full range-of-motion movement of an exercise (e.g., standing dumbbell bicep curl, barbell row, standing dumbbell lateral raise, etc.).  It becomes noticeably apparent when one deliberately hitches the weight upward by utilizing a jerking movement.  
    If you choose to decide to cheat in order to complete a set, be sure to do so only during the tail end of the last set of an exercise.  In other words, cheat only when you're very close to muscle failure.  Muscle failure occurs at the point during a set when you would not be able to complete another repetition by yourself even if your life depended on it.  Then, and only then, is it permissible to cheat when performing an exercise.  The purpose of cheating in this case is to take a muscle slightly past the point of muscle failure and into the realm of near total muscle fatigue.  Maximum muscle fiber destruction occurs at this point in which the goal is to gain more strength and muscle mass.   

    The answer to this question largely depends on your anaerobic fitness goal (i.e., weight training goal). There are essentially four goals when it comes to weight training:  

1. Maintain physique (endurance training)
2. Gain muscle mass (mass training)
3. Increase strength (strength training)
4. Increase power (power training)

Whichever goal you choose will determine how much rest or recovery you should take between exercise sets. Each of these goals is unique with regard to the following parameters involved:

• Load intensity (i.e., percentage of one-rep max)
• Number of reps (e.g., eight to twelve reps)
• Movement speed (e.g., slow, moderate, fast)

Let's take a closer look at the recommended parameters for each fitness training goal:

1. Endurance training
• Load:  < 67% 1-RM
• Reps:  > 12 reps
• Speed:  Moderate
• Rest:    30 s
2. Mass training
• Load:  67 - 80% 1-RM
• Reps:  8 - 12 reps
• Speed:  Slow
• Rest:  30 - 90 s
3. Strength training
• Load:  80 - 85% 1-RM
• Reps:  6 - 8 reps
• Speed:  Moderate
• Rest:  2 - 5 mins
4. Power training
• Load:  < 45% or > 85% 1-RM
• Reps:  > 30 reps or < 6 reps
• Speed:  Fast or slow
• Rest:  2 - 5 mins

    Rest periods may vary from 30 seconds to 5 minutes depending on your fitness goal regardless of your weight training experience level.  Generally, the lighter the weight lifted, the less the rest period and the heavier the weight lifted, the more the rest period.  
    During resistance training the muscles fill up with blood as the body delivers nutrients and removes waste products.  Active rest, in which the muscles continue to contract and relax while under low resistance, will allow this process to be more efficient and therefore enhance recovery.  Thus, it's better to continue moving (e.g., standing and shifting your bodyweight from one foot to the other) between sets rather than just to sit still and allow blood pooling to occur.