There's probably no other pursuit that people enter into with more ignorance than lifting weights. If you wanted to plant a garden, you wouldn't just throw some seeds aimlessly in your backyard and pour water on them. If you wanted to tune up your car, you wouldn't start tooling on it with a monkey wrench and hope for the best. That would be stupid, right?
- You have to follow the law of progressive resistance. This isn't optional. If next week's leg workout doesn't find you lifting heavier weights or performing more total reps than this week's did, you wasted your time. Your body is placed under no extra demand, and will not change. The same goes for cardio. If you don't run harder or longer, you don't get leaner or more cardiovascularly fit.
- You have to train the whole body. The sport of bodybuilding has poisoned our minds with the notion that we have to do just arm exercises to train the arms, just leg moves for the legs, and if we don't regard our backs as a priority, we can give them much less attention or skip them entirely. Wrong. If you get nothing else from this post, let it be this: it doesn't matter what your ultimate goal is (big arms, a flat stomach, a 400-pound bench press), you have to train every major muscle group with equal enthusiasm to get there. Don't like doing squats? Tough. I bet you don't like being fat and weak even more.
- You must keep a log of what you do in the gym. It's the only way to know for sure if you're beating your old records. You should also take measurements to see if your waist is shrinking/muscles are growing over time. Otherwise, you're just guessing. Things you think are working could be doing nothing. Things that are working you may not even notice. Take a pen and a pad or notebook to the gym and write down sets, reps, rest periods, weights you used, levels on the treadmill you got to, etc.