There are a few factors that contribute to how big you blow:
Going for a few days without cumming will increase it.
Edging for as long as possible before the main event will increase it.
Herbal supplements such as L-Arganine and Lecithin will increase it (might want to look up around the Supplement and Health forums for these and many others).
Also training your PC/BC muscle will increase it.
RoP (Ring of Power) will increase it.
Also there are a bunch of commercial supplements etc. I'm sure I've forgotten something but these are the most frequently mentioned in my mind. You can pick any of these to go with but if you combine them all, woah, tell 'er to wear a snorkel. Good luck!