A good way to stretch your hamstrings (especially if you are tight) is to just put your legs out straight and then sit up straight while pointing your toes to the ceiling.
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Once you get better at sitting up straight you can practice doing the same thing but leaning forward. You can also try putting one foot up onto a stool or chair and then leaning forward into the leg that is up so that you feel the stretch behind your leg and up into your bum.
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