I started lifting weights way back in high school, and it became a semi-regular form of exercise that I would do when I wasn't involved in team sports.  I kept at it through college and into adulthood, and although there have been some (long) periods of time when I was not able to lift, it's something that I gravitate towards when I feel the need to get back into shape.  It was only in the past 2-3 years, though, that I realized I had been going about it the wrong way (or at least partially wrong).  I started reading up on articles on weight lifting which challenged me to rethink some fundamental things I had been doing (or not doing) and now I better able to maximize my workouts.  Here are four simple, yet key things, that I wish I knew back when I started weight lifting years ago.1. Work your whole body, not just upper bodyFor many years, I concentrated almost solely on upper body strength when I worked out - biceps, triceps, chest, back, abs, traps, etc (all areas of the body that are easily seen in a mirror).  I might do a few calf raises some time, but most of the time my focus was on things like dumbell curls, bench press, lat pull downs, and so forth.  It was only recently that I discovered the need for doing whole-body workouts, including legs and back, as part of an overall strength-training regimen.  Think of it - by working out the huge muscles in your legs and mid section, not only is your body able to consistently burn more overall fat, but you are also working muscles which are much more practical for everyday living.  One of the best exercises for this is the squat, where you are working your entire lower body all at once.  Although the results aren't necessarily going to be highly visible when you look in a mirror, they'll help in non-exercise activities such as moving furniture or picking up heavy items.  I think that squats and other similar exercises make you stronger in a more holistic way than working out the upper body alone.2. Focus on compound exercisesOne of the appeals of working muscles like biceps is that the results can easily be seen both in and out of the gym.  Therefore, I tended to give these an elevated level of importance in my strength training by doing lots of curls.  Now, however, I am starting to lean away from this approach, and instead trying to focus on compound exercises which work entire muscle groups, such as squats, bench press variations, and cable row.  Compound exercises are more helpful since you get more benefit from the same amount of work, and because they work all the small muscles in your body that you may use in activities but which cannot be easily "worked" on their own.  You basically get more bang for your buck with these exercises than you can by focusing on isolation exercises alone.  While there is still a benefit to isolating muscles, there's a limit to how much time and energy you should put into them.3. Rest a muscle group for more than two daysThis was something which I missed for a long time.  All the way back in high school, I was told that you alternate workouts of specific muscle groups every other day since muscles need time to repair.  When you exercise, muscle fiber breaks down and is subsequently repaired during your time of rest, making you stronger and ready to work out again in the near future.  While this tip was good to know, I think I might have underestimated the value of rest, and I have now come to the conclusion that muscles benefit from more than just 48 hours of inactivity.  By giving specific muscle groups at least three days of rest, I give them a much better chance of making 100% recovery than if I only gave them two days of rest, which might only result in 90% recovery.  This way, I am not breaking down muscle fibers which are still trying to recover from my previous workout, which seems to be counterproductive.  Today, I am able to give specific muscles a rest by alternating workouts correctly.  So if on Day One I workout chest and triceps, on Day Two I workout legs and on Day Three I workout biceps, upper back, and shoulders.  I then go back to Day One workout.  4. Protein and diet matter a lotLastly, I can remember back in college when I was at the peak of my weight training and was able to bench press just over 300 lbs.  The funny thing is that eating protein really never crossed my mind.  I do recall drinking a lot of milk, and eating meat, but I didn't make a conscious effort to target protein in my diet.  Today, I recognize protein consumption as one of the most fundamental ways to make advances in strength training.  Specifically, I target the time just after a work out as the optimal time for eating it, such as in the form of a whey protein drink.  It is at that time when muscles are very ready to absorb protein to begin the recovery process, so I find it the single most important time to consume it.  While I admit that there's a lot of nutrition information about bodybuilding out there which I either don't understand or don't care to follow, I do think that eating sufficient protein is the one practice that needs to be done to make strength gains.  Had I known more about how to eat to support my workout back in the day, my gains could have been all the more.  In conclusion, these four things would have been helpful to know years ago when I started out weight lifting.  They aren't rocket science, but they aren't obvious, either.  Do you have another approach to strength training that you think should be on this list?  If so, add it in the comments below.