I was once told "if you always do everything the right way, you'll never do anything the wrong way." I think that means just don't get rushed or careless.
Whatever you do, don't leave your old job before you have everything in place to have you business up and running.
We could have a 40 item list for this but it's main items would be company name (inc - to protect yourself), a website (and register close names to it to keep the competition from rereouting people to theirs), a easy to remember phone number, a logo, all licenses in place, all insurances in place, Invoices and business cards printed, a truck (preferrably paid for), some ads working for you and perhaps join the local chamber of commerce to mingle with other business people.
My first move was to buy the book "how to start a small business" from amazon.com.
Best of luck.
