The reason I have emphasized "written" is because if you don't write your goals down they are merely wishes. Studies have proven over and over that writing your goals down is powerful.
Let's look at some examples. If you want to get back into running, walk first. Depending upon your level of fitness you may only start with fifteen or twenty minutes. If you have some level of fitness start with 30 minutes and gradually increase it.
Once you have been walking for a couple of weeks ease back into running by alternating walking and running. Walk for ten minutes and run for five and so on. As you increase your level of fitness and your soreness lessens increase the running until you get back to running for thirty to forty five minutes at a time.
If you have been involved in weight training in the past and have taken a layoff of more than a couple of months you really need to take it slow coming back.
With weight training, if you push to hard to early you can end up damaging supporting tendons and ligaments. The key is not to rush in trying to use the same weights you were using and do less sets.
What I do after a long layoff is go to the gym and ride the stationary bike for 15-2o minutes first to warm my body up. Next, I will choose only one body part per day to exercise. If you are an older person or have a larger frame you may want to continue this type of program even after your initial break in period.
Let's look at working the chest for example. If I were bench pressing 300 pounds prior to my layoff I will begin my first work out with 135 pounds and do 3 or 4 sets of high reps in the 15-20 range. Adjust your weights accordingly. Then I may do 3 sets of flat dumbbell flyes again with higher reps so as not to place to much stress on my tendons and ligaments.
Follow these same guidelines for all body parts and increase the weights and reps slowly and within a month you will be right back to hard training again and working towards your goals.