One little trick that works for me is to balloon out the main vein that leads to your dick, between the anus and balls. If I’m not 100% confident of being able to get rigid enough here’s what I do. A few minutes before I need to perform, I work myself up to as hard as I can get, at least 50% and no need to be 100%, and then I squeeze my dick hard from the head down, so that I can feel the pressure built up in the taint. I might do a couple long squeezes but no more than 5-10 seconds, mostly some pumping type action, whatever feels right. I’ll throw in some kegels for good measure.
It may be a purely individual thing, but hey, it works for me. After pumping up the taint a few moments, I can let the erection go down if necessary and go start the love making session. Then when it comes time to rise to the occasion, I think I just have a better flow in.
An erection is a two part process: the veins that lead in expand and allow more blood to be pumped in than usual, and others shrink to slow the outflow. I don’t know if you can improve that second function but you may be able to help the first.