Personally I have a playlist which is configured to exclude all video, all podcasts, all really long tracks, and various albums and genres I don't want included unless I specifically add them - classical, some film soundtracks etc.
From that playlist I then have smart playlists that are based on the various ratings: 1, 2, 3, 4, 5, 3+ and 4+.
I also have playlists for songs I haven't listened to, that I haven't rated, that have been recently listened to, that have been recently added, the most played, that haven't been listened to for various periods, songs under 3 minutes, songs from different decades and so on.
I also have combinations of those playlists, for example: songs that are rated 4 or more and that haven't been listened to in the last 2 months and various other combinations.
I can then change what playlists are synced so that I don't fill my iPod up too much - but also so that I don't have to wade through low rated songs whilst I'm out and about.