1. Set a time limit on all your workouts. End the workout if you run over.
2. Exercise larger muscle groups before the smaller ones. I.e... Back, Legs and Chest before shoulders and arms.
3. Change your workout plan up every twelve to fourteen weeks.
4. Treat your time in the gym as if it is your most important time of the day.
5. Make the workouts at the beginning of the week harder than those toward the end of the week.
6. Take at least one day off a week from doing any form of exercising.
7. Change your cardiovascular equipment up each time you exercise.
8. Monitor your heart rate all the time.
9. Go over your workout in your head before you start.
10. Efficiency is more important than length. Have a number of reps in your head before each time you do a set.
These are just a few things I have learned over the years. Do not be afraid to try different things. Listen to your body and never be afraid to ask for help.