The best method is simply to avoid ejaculation for several days or even a week prior to the event.

Some have mentioned methods an increase in fluid intake, but the avoidance of alcohol and caffeine.

You can APPEAR to increase your output by removing the cover and elongating your penis as you ejaculate, enhancing the nozzle effect.  Done properly, you could qualify for the shot-for-distance competition.

Mostly though, just let it build up as I said above.

using a cock ring?  It increases the force of the ejaculation and you will orgasm like never before - both you and your partner will feel the difference in the forcefulness.

I have never had a problem with quantity or forcefullness in my "finishes".  I can usually squirt at least three feet and most of the time more.  I think it has to do with the fact that I jerked off when I was younger probably 3-4 times a day (I was a virgin until 21).  I can come in the AM with great quantity, and then still produce a great quantity at noon the same day if needed, and then still orgasm that evening quite well.

I have not noticed the quantity or delivery changing since I have gotten older (I am a little over 40 now).  Since it is delivered via muscles, I really think that since I worked those muscles when I was younger, they are in great shape now (The only part of me that is in great shape )

Perhaps that is why some call me the "Cum King"!

All of the male porn stars I know eat a great many eggs before they work.

There also some supplements that can help. One Zinc tablet per day along with two Lecithin gel tabs per day have increased my load.