Mudokon Pens
The first level where you have to switch between Abe and Munch. Always keep their individual strengths and weaknesses in mind - Abe is good on land but sinks like a stone in water, Munch isn't too fast nor can he jump high on land but he is at home in water. So while Abe can't cross over at first, Munch can - so use him and then once you are over, you should be able to find a way to activate the Travel Well at the point where Abe is stuck. Can't figure out how to open the locked cages with the Fuzzles and the Mudokons? Munch can use his zap-ability to free the Fuzzles and they can take care of the slig guard inside and open the doors - simple

Then you have to get through the doorway blocked by explosive boxes - use Munch to get upto the remote on the hill and then use the crane to get rid of the explosive boxes blocking the path as well as the slig guards inside. So how does Munch get up to the crane? Notice the three chanting circles on the dock? Get the Mudokons to chant there to open up the Travel Well in the water and then Munch can use it ... Still stuck after getting Abe and his buddies in to the blocked area by another blocked doorway? Notice the little ledge in this area up on top? Maybe the crane can take somebody (like perhaps Abe :p) up there? The rest should be pretty simple ... except perhaps about how to get to the next level - just have Munch and Abe (both) stand on the teleporter at the very end of the level to get to the next level.