Qualification questions

Hello people I'm a recently new turker and its going great right now! (thanks to HWTK) But I would like to hear from some veterans about qualifications. I know some thats pretty much standard (adult 18+) but I am curious about more. I know some good HITS require some quals but how do I know about getting worthwhile qualifications? Is it just luck of the draw when searching for quals that will last for many HITS or something else? I know alot of the 'write X amount of words for article' have qualifications and if you want to talk about that I am still interested but are there other ones that help out just as much - or are randomly offered that can open up many HITS? Thanks in advance