I don't rename myself but maybe for a start picking something you might like may be a good idea.
Renaming new stuff (adding sets) is also a bit tedious because most of the "common" software is already in and although many unrenamed sets exist, most of them will probably be alternate versions, hacks or bad dumps i suppose. A different case might happen with some really weird and obscure systems but you will probably need a lot more knowledge about the systems and emulators many time sucks or don't "exist" yet. That way, the current work is more focused in fixing/verifying our current dats/sets cleaning many errors.
Still, there are a few systems in our database that are very incomplete but i don't know who is working on them (Atari 2600 comes to mind, when i entered the project the dat was being redone but the work stopped and we now have an half done dat). There is also some work to do, reorganizing existent dats, eliminating the "Various" dats and putting their sets in the right place (Applications, Games, ...).
Anyway it is not always easy to start working in it, my suggestion would be for you to read the naming convention and ask anything you need until you understand it correctly, after that you might ask one of the current renamers (TKaos, Cassiel and others) and maybe they need some help that will guide your start.
IMHO, after reading and understanding the TNC, a nice way to start that would help us a bit and also be less tedious / more fun, would be verifying our dats and adding information to what we have now, this is mainly done by checking which publishers, groups, persons, etc. are valid and which are not. So they may be fixed later. Unfortunately this work depends on some "tools" that are currently not available but i will bring them back sooner or later (free time needed

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