make yourself some templates, especially a Mickey head. Make sure it is very clean. I have seen some people post DISigns where the Mickey head had little, what I will call spikes....not smooth at all. This really takes away from the professional look. Clean it up once and the work will be worthwhile. I have one I call BESTMICKEYHEAD.jpg and everytime I need a Mickey head this is there for starting the image. Simply cleaned up black head....no spikes and no halos of extraneous colors.
stay organized....be sure to bookmark (or make favorite) your favorite clip art sites. also organize your own files so you can easily locate things. I have a clip art folder on my hard drive that has subfolders for characters. If I need an Ariel, for example, I know right where to look. Halloween clip art? They have their own folder as well.
if I find a clip art image that I don't need immediately I still save it and will have when a request pops up and it is the perfect fit.