I go through phases of doing yoga quite frequently and then stopping for a while and going back...
I've not noticed any real differences when taking up yoga, it does help with stretching but I do that anyway after running.
What I have noticed when it comes to helping with running was working on balancing exercises. You don't need to spend hours doing them and you probably wont notice any differences the first few weeks but if you can, things like standing on one leg, then on a bosu ball, then with your hands reaching skywards and gradually moving around to create more of a challenge and then with your eyes closed and head upwards...there are many variations and the important thing is to not develop a stratagy (so none of this "I'll just stare at a fixed point" stuff) and to work on making your core stronger and acting as something to keep your balance (rather then your eyes!).
I found it had an impact on my running after I did these core stability exercises for a good 5 minutes to 30 minutes a day and at least every other day if not ever single day.