My thoughts on this are a little different from what I think the usual:
The most common approach seems widely to be treating this as a mechanical issue. For example, okay, more nitric oxide means more erection so what mechanisms can result in more nitric oxide.
However when I first started trying this sort of thing, I found that with repeated use, soon effect with Viagra was exactly the same as it had been without. Fortunately, rather quickly effect without Viagra was soon back to same as usual. So basically I decided the Viagra was pointless (in my case) though it seemed likely that if used a small percentage of the time, those times it would be effective.
This had me thinking that undoubtedly there is a feedback mechanism. The body doesn’t simply try to create an erection absolutely as hard as possible. In fact it’s pretty painful to be at absolute maximum for any extended length of time. Better is seriously hard but not absolute maximum. So there has to be a regulatory mechanism.
This mechanism may not necessarily regulate to what we consider a correct level. If that’s the cause of the situation, then long-term, things like Viagra aren’t going to work because the body will learn whatever adjustment is needed to regulate to the level it thinks correct.
In another thread just the other day it was discussed also how anabolic steroids very often despite giving increased libido for some time such as say the first 6 weeks, not unusually this will taper off and libido may be same as baseline by say week 8. That could be a matter of learning, or possibly slow biochemical change. Anyway some time off soon results in increased effect again.
Probably the key is the nervous system.
It’s probably going to be different individual to individual what herbs may help. Obviously Tribulus is a big seller for that purpose; does nothing for me. However for anyone that it does work well for, or a combination product such as Alpha Male does, then that’s what counts, that it works for that person. Other herbs that may be likely to work are, as saps said, maca; and maybe to some extent catuaba, schisandra, and muira puama. Vitamin Shoppe has a reasonable combination product labelled as Horny Goat Weed but actually containing that plus maca and a couple of other things.
Saps mentioned using a SERM: this has the effect of increasing ejaculatory volume and if not using steroids may well help by increasing testosterone.
For me the most effective is androgens when not already on them for some time.
Androgen use should not be expensive especially if limited to just the Proviron. If there’s any predictability to when more performance is called for, there would be, I would think, no use in starting more than 2 days early. And it may well be that that might be no better than just an hour or couple of hours before. I have only used it that last way, rather than in the couple of days before. But with regard to other androgens I’ve noticed that the best effect is not the very same day.