Start with jelqing but add Kegel exercises and stretching as well.
Just stick with those three for several months and see what the result is.
There are lots of more "advanced exercises" and some guys go on to use some type of apparatus, such has a weight hanger, air vacuum pump, water vacuum pump (like the Bathmate), or extender. But if you see gains with manual exercises, I would stick with those as long as you do.