stretching:
grab in the groove behind the head either overhand or underhand grip, whichever works best, and pull. Some recommend pulling in all directions, I just pull straight our or down. The use of baby powder or talc can help with getting a good grip.
Jelq:
get a semi erection (your penis should still be easily bendable), take an overhand grip and make an ok sign close to the base of the penis. squeeze and pull towards the head. Think of squeezing the contents out of a linl of fresh sausage. You should feel the blood move forward, your head will puff up some. 3 sec jelqs - 100 strokes should take about 5 min. pause to fluff up when you are too flaccid, pause when you are too erect.
Kegel:
it is the same muscle you use to stop a stream of urine, your asshole will also get into the act to some extent, try to focus on the penis part though and although you cannot totally inhibit the anal sphincter, try to not rely on an ass squeeze too much.