Well, first off, you need to learn how to spell. Just kidding.
First, you should go into a dungeon. Choose an easy one like Purple or Green. Yellow has a boss at the end which you should only choose if you're going with a team or know how to do. Red is hard so don't go for that one.
Second, just explore. There's tons of secret places in the map that hold treasure. Keep looking and grab as many coins as possible.
Third, kill every monster you see and loot their corpse. It's a bit grim, yes, but it will give you bullets and coins! (Or "moeny" as you'd say)
@Derpagonair thank you for this guide!
I'm glad you still play Cube Cavern, even after all these years! But your reply was kinda late, y'know?