The qucikest way to increase your skill points is to play a mini game. The harder the level, the more resources you get - however the maximum amount of skill points you get per game is 50.

As such if you go to the double up hut (in section 3 of the island and looks like a huge hut/casino) and play a four card game, you can easily win this without burning too many braincells. It is also an exceptionally quick game and you can easily get 1000 skill points in about 5 minutes. You don't need to play a harder level as you won't get any more skill points.