Brainstorm. Think of things that you are interested in. If your mind comes up blank, take a interest test from the internet. This will get some ideas flowing.
Step2
Look for things that people do in your area. Go to the park, watch people play tennis, softball, basketball, jogging, biking, soccer, football, ect. By watching other people have a good time, it will encourage you to find something that you would enjoy doing, and do it.
Step3
Find more then one thing that you would like doing. Having multiple options gives you more opportunity to do what ever it is that you like to do.
Step4
This step is important. Try new things. You will never know if you like to do something until you try it. And not just try it once, give it a chance to grow on you. If it doesn't grow on you, then its probably not something that you are interested in pursuing.
Step5
After you have found some activities that you enjoy doing, do them. And the best way to do this is to make a schedule and follow it. Even if it is only for a hour or two after work, go do an activity. Having friends or siblings to bring along with you is also helpful.