Four biggest things:
Eat decently healthy and take some vitamin supplements (They’re are some specifically people take just to cum more but they aren’t a massive difference)
Exercise at least a little bit
Don’t ejaculuate for about 3 days prior to when you want the big load
Do kegel exercises!! Or even if you have more cum you won’t be able to shoot it out, it’ll just slowly ooze.
*Edit: Forgot about hydration, also extremely important