Create an 18 Hole Tournament at Bandon Dunes in your Country Club (red tee's). You get 400 XP for finishing + XP for each swing + XP for CC bonus (bigger the CC the better).
Invite 1000 friends over to your house and have them bring their lap tops. Being a good host you should have Spirits and Food (mandatory!!). Talk some smack and have a good ole time. At some point, after they are happy you put them to work.
Have everyone pull out their lap tops and log onto your Wgt name. You go and purchase a 1 hour WGT XP Ultra Boost. Everyone plays three 18 Hole Tournaments on Bandon Dunes never hitting the ball off the tee (9xp per hole *18 (162)+400 (Tournament XP) + CC bonus (around 20) = 580 total XP). Obviously use starter balls. The math looks like:
1000 friends * 580 (total Xp from one 18 Hole Tournament) * 3 (number of rounds played) * 1.4 (40% XP boost) = 2,436,000 XP. That's enough to go from level 0 to Level 100 in 1 hour.
Seeing how this scenario would never actually happen ^^, I suppose the best way to level up is to create an 18 Hole Tournament on Bandon Dunes and get around 580 XP every time you finish (don't hit the ball off the tee). You should be able to comfortably get around 2000+ Xp in one hour.
People have been using this Xp gambit forever. Do make sure to lower your flash player to Low (not Hig, Medium, or Best). If you don't you will get severe game lag and long delay's necessary between shots.
Cheers.