at the beginning i only used keywords and smart collections. i don't favorite first and then assign a keyword - that sems too much work for me (but i use the favourite and reject - label. favorites for, em, favorites and reject to weed out bad clips). i usually have some smart collections that i copy from project to project, e.g. "audio only" , "images", "multiclips"...
now, before i start with keywording, i use the clip info to label everything with camera, scene & reel first - that gives me more options to sort clips later. (as max girth said: don't get to specific, better combine later)
i also work hierarchically, starting with the more common keywords and go into details later.
i don't use the notes section and roles only, when i have to render a clip with multitrack audio or export to logic. sometimes i use the automatically assigned roles for quickly turning audio off (e.g., when i'm color correcting and listening to music from itunes). roles can also help you to get a quick overview over your timeline.