This was from a legal perspective, and a good one at that, but I was also thinking of:
Health care stuff. If you're due for new glasses, braces, try and get it in before you quit your "normal" W2 job. (And of course research health care stuff before you quit, related thread here: http://news.ycombinator.com/item?id=560169 .)
And by "health care stuff" don't automatically assume that means insurance. If you require prescription drugs, research the price of them. Some drugs cost hundreds, others you can pay closer to $20 for a 3 month supply. Sometimes there are alternative drugs for the same condition that aren't normally prescribed, but work just as well--dessicated thyroid for hypothyroidism instead of levothyroxine, for instance. See how much you can afford paying for out of pocket or out of HSA before thinking about what kind of benefits you want from insurance.
1. Save up lots of cash
2. Get rid of any junk debt like car payments, store cards or credit cards and cut your expenses way down
3. If you have a significant other, make sure they are very understanding and supportive, because times will get tough
4. Read and understand all the legal stuff and get it right from the get-go
I don't see anyone else mentioning a line of credit - when you're young and without many assets, it's easier to apply and get one while still employed, and perhaps a bit more flexible than a credit card. I definitely having one useful a few times when cash was tight starting my company.
* Have some savings (I quit with above 1 year or rent)
* Have equipment, backup drive, laptop, and ec2 (servers)
* Setup some ways to quickly get moving Wiki, Blog, Github, Ticking System
* Have a layer to help you incorporate and deal with anything that comes up.
We quit having a few ideas and not knowing which we would start with. I guess if you aren't in a rush I wouldn't quit until you had the idea you really wanted to start working on.
