Running beginner -stretches for preventing shin splints

The biggest tip for avoiding shin splints is not to increase time/distance too rapidly and get good shoes.
For warm up I do about 20 calf raises before running and walk on my heels for about 30 seconds. Sometimes I also do feet circles to warm up my ankles, you can do this or flex and point your feet. After the run and cool down do a more static stretch. If you stand on a curb or step with your heel hanging off it's another good way to stretch your calf. You can also do a calf stretch by getting in the position of downward dog and put weight on each foot stretching the calves separately.

Good luck!

Yup, shin splints tend not to be a muscular injury, so stretching won't really do much to help them. They're more a stress injury, most often caused by - as others have said - too much too soon, or wearing unsupportive shoes.

If you're doing the Couch to 5k program, great. Just follow the programme and make sure you take the rest days to give your muscles and joints time to recover. I agree with MeanderingMammal re: shoes, but it's worth stressing that you probably shouldn't be running in pumps or 'fashion' trainers. Even if you don't want to invest in a decent pair of properly fitted specialist running shoes to start with, I still recommend picking a good, cushioned cross trainers to get started. When you start running further, get yourself to a specialist running shop and have someone assess your 'gait'. They'll put you on a treadmill and watch/video you run, then recommend the best shoes for your feet.

Back to stretching, which won't really do much for shin splints, but is still important to avoid other injuries, try not to do 'static' stretches before a run - save those for after. Instead, warm up your muscles by doing 'dynamic' stretches or gentle jogging for a few minutes. By 'dynamic' stretches, I mean 'moving' stretches like swinging your legs out in front and to the side, rotating your shoulders, jumping up and down, calf raises etc, as opposed to 'standing still' stretches like pulling your foot to your bum to stretch the quads, or sitting on the floor and reaching your toes.

You can do static stretches afterwards to smooth out the muscle fibres and ensure you don't tighten up. Make sure to hold em for a decent amount of time!