Try drawing yourself a branching diagram or flowchart that shows everything's relationships.Start off with some common ancestor, then split that into eubacteria and archae. Put a box above them labeled Prokaryotes and put some of the basic prokaryotic characteristics (no nucleus, etc) and then under each one's name put their unique characteristics. Continue the line from Archae and branch it out into the other kingdoms, passing all of their lines thru a box labeled Eukarya and put the basic Eukaryotic characteristics in that box. Under each kingdom's name, put their basic characteristics, and create whatever branches are needed (Protozoa, algae, fungus like protists for the Protista, for example). Remember to put the most memorable/unique characteristics first. Try to see the trends, such as the more "simplistic" organisms being haploid, "complex" being diploid. To study, cover up part of the diagram and try to remember it, rewriting it 5x if you're wrong.