There are a lot of exercise, find one that you enjoy. You can also search videos
Stretching exercises are only performed when muscles are warm and the body temperature is raised. stretching involves applying force to the body’s muscles, which must be held just beyond a feeling of pain and needs to be held for the correct amount of time(20-40 seconds). If held too long, the muscle will become too loose and stretchy.
Have you checked into yoga? Yoga has many benefits and will increase flexibility.I am researching how to improve my flexibility for a project for school and would appreciate any helpful tips and information on the topic