The idea is to stop the paint drying in your pallete, lid, jar and to loosen up the surface tension that gives you the big blobs.
You can use a thinner to reduce the thickness of the paint, as mentioned put the paint onto a palette (plastic lids work) or you can try a retarder.
Tamiya do one for their acrylics, there are lots in the 'art' section of the craft stores.
Personally I use the Badger Minitaire stuff for acrylics.
It stops the paint drying as quickly and gumming up