Are you asking for credits or XPs (=> levels)?
For credits, the best way IMHO would be to get out of the house, earn some bucks and spend them for credits. The wage by the hour is incredibly low in WGTland!
For XPs, it would be to play at least one hole in 24 hours to get the CDP bonus. Next, play tournaments for XPs. Multiplayer games are good for the fun of it.