The mistake that most new boaters make is running the engines too lean. When you fire it up you want a slight lag when hitting the throttle. When the boat hits the water, the load of the prop will lean it out.
Make sure that you use fuel made for boats, not planes or cars as it doesn't have enough il content. You want 18-20% oil. Don't be afraid to run high nitro either as most of us run 40-65%.