Some tips in keeping a man's fitness level high, efficient and safe:
1.) Drink plenty of water all through out the day, especially when working out.
2.) Do exercises properly using the correct techniques, whether it's weight lifting or aerobic exercises. Always read and understand, and follow of course, the instructions outlined by the personal trainer.
3.) Make sure the is always a spotter when lifting weights.
4.) Challenge the muscles, but make sure that it's kept safe.
5.) Stretch, warm-up prior to working out and cool-down gradually after sessions.
6.) Check the equipment for safety before using them.
7.) It is better to do less than overdo the whole thing. Overtraining will exhaust enthusiasm and kill performance.