While taking warfarin means you need to be more careful, it doesn't mean you need to wrap yourself in cotton wool!
It is important to think about the activities you like doing an ask yourself "does this put me at risk of injury?" If the answer is yes it may be best to try another activity. For example, contact sports, or any pastime that causes knocks, bumps or bruises, are usually best avoided.
There are many activities which you can still participate in safely, such as walking or swimming. Other activities, such as riding your bike, can still be safe, you may just need to remember to use protective gear, such as a helmet and gloves, while you are doing it.
The other important thing to note is that changes in the amount of exercise you do may change your INR. Discuss any plans to start a new activity with your doctor.