You should participate in a variety of activities each week. Concentrating on one activity or sport can lead to activity-related repetitive injuries. Always use proper form. Slow controlled movements are often best. If you're unsure about the proper form, consult a trainer to give your workout a check up.
Many people underrate the importance of warming up and stretching.
Before your workout, spend some time jogging in place or doing jumping jacks to warm up your muscles so that you can stretch them easily. Never bounce while stretching and never try to stretch without warming your muscles up. If you play a sport, learn the proper techniques required by that sport. Improper technique is linked to recurrent overuse injuries. If you are unsure, take lessons or consult a pro.