here's one walter gave me - *after* i really needed it...but that's not his fault! if you don't have enough air in your lungs to purge a reg, make 'clicks' with your tongue until it clears.
my second tip is - dive. dive anywhere & everywhere. dive in the local boring quarry or lake or ditch or whatever. practice everything. go for zen, shoot for perfection, try new stuff, all of it. many folks spend the first several dives of an expensive dive vacation working out a lot of bugs, but by diving frequently, you'll have a very short list of issues in new places.