Take a day off each week. This will allow your body some much needed rest, but it will also give you a chance to think about something other than fitness for a while. That way, you can return to your fitness program with fresh eyes to see if you'd like to try something different or want to change a few things.
Don't exercise on a day when you aren't feeling well, or haven't had much sleep. If you do, you'll find that your workout isn't as satisfying because you won't be able to put 100% of yourself into your routine. Take a break and return to exercise when you're feeling better.
Most people will work out until they reach a certain goal. For a lot of people, it is the amount that they can bench press. This is called maxing out, but you should not max out on a regular basis. You should test it out only once every month.
If you're trying to encourage your kids to exercise, make sure you don't push them to do too much too fast. Try to build up the amount of exercise they're getting. If they're used to be couch potatoes, try starting with something easy like biking or swimming, instead of having them run two miles. If they feel it's too hard from the get-go, they'll dig their feet in and try and fight you.