
Some common conventions used are sans serif font, all caps, silly spellings of words (HAI for hi, Bai for bye), exclamations, and many captions start with "IM IN UR VERB, VERBING YOUR NOUN." The caption is basically a speech balloon or thought bubble of the cat in the image or a description of the image. It often reads like baby talk specially since a lot of the cats in the images are kittens. Here is a brilliant LOLCAT example. You can find lots of these on the popular ICANHASCHEEZEBURGER.com and image sharing sites like Flickr and Photobucket.
