I'm rather ignorant when it comes to mods, played only a few of them and they weren't that good.
Is there some kind of a big website filled with mods for all kinds of games, or do you just fish out different mods, for different games, from different parts of the internet?
I would also suggest downloading Desura from the website. It's steam-inspired client, except it's for mods and indie games - basically, you can easily browse best and most popular mods from MODDB there, and if you want to try a mod, it automatically detects installation of the base game, and then downloads / installs the mod, hassle-free. Uninstalling a mod is just as easy.