You should probably do the plumped bend that most people appear to do.
Take your primary horse grip at the base and wait for the erection to subside so that your penis is plumped but not erect. If you can, kegel in more blood releasing the grip slightly as you kegel. If you are pumped enough there is no need to apply the second part of the horses grip just bend the penis in a gentle curve applying the strain with the second hand until you feel the tissue stretching and hold for up to 30 seconds. If you find your penis not bending in a gentle curve but rather seeming to bend dramatically in one small section stop, you are probably too erect.
Release, the bend and repeat in a different directions. Between each bend release the base grip a little and kegel in some more blood.
This is not a newbie exercises but without the application of the second grip its certainly less hard on the surface veins than a horse. As with anything take it easy when you start.