I come to you now, and bumping up a super-old thread, after finishing my first week at my first official full-time job in my new career.
My advice, in addition to the stuff I posted earlier in the thread, is this:
Tip #1: Give yourself time and options. If you don't know what you want to do or there's no clear path to get there, the most important thing is to give yourself the chance to make good decisions in the future. What I mean is, to learn as much as you can, but more importantly,
save up as much as you can or be militant in your time management, if you can't save. I know another person who made a similar, although less random, career change, and she managed to work full-time in her old career throughout, before making the jump. That's safest, although crazy for her schedule-wise. I had built up quite a bit of savings at my old job, so after I quit/was pushed out of the lab (Congress doesn't care about cancer research since our grant was sequestered!

) I didn't
have to take the very next place that would hire me. That's extremely important.
It IS a luxury, I know, to enjoy what you do. But if you're going to choose your career, might as well make the job as enjoyable as possible. Give yourself the chance to work at a place you like, doing stuff you like, with people that you like, for enough money that will sustain you. It often won't be the first place you come across.
Tip #2: Be proud of your past. I came to design from science. I didn't have much formal design education - I cobbled together what I could, education-wise. A lot of people would advise not mentioning much of my science background, because that could show that I wasn't "committed" to design. I decided that opening with, "I used to do cancer research" would intrigue people, because it actually did.

I'm also a designer who can code, and many people would advise not spreading myself too thin. Jack of all trades, master of none, right?
The place I'm at now, they actually WANTED me because I had a science background and could code. I knew early on, that going for a startup would be my best bet, because startups often look for people who can do a bit of everything, especially code. But my research background is something unusual they liked, because A) I would be handling a lot of complex programming/science concepts when designing the software, and B) half of the team had a biology background of some kind. Me being a fellow scientist was important to them, even if it wouldn't be important to anyone else, literally.
Even if you had a sh***y service job before, be proud of that! There was a super-famous design firm recently looking for a junior designer, and they specifically said they wanted someone who, in the past, had worked a crappy job waiting tables. That puts some hair on your chest, that someone coddled in high school and college (like me) doesn't have.
If you're going for a job that requires you to be more than merely a butt in a seat, who you are as a person does matter to someone. It isn't that you should be something for everyone, but you'll be an important someone to one company or team. That's the sweet sauce.
But this is Tip #2 because waiting for a company who truly appreciates you, often can't happen without having done Tip #1.
Tip #3: Know when you can do better. Don't get me wrong, I've done some crappy freelancing jobs in the past. I've done so much free work and a ridiculous amount of personal side projects. Saying no to every situation if it isn't perfect, is not the way to build up life experience, or experience in general. You will learn something from everything you do. But that doesn't mean you should relegate yourself to a crappy job and think that's all you can look forward to in the future.
Know what is important to you, and don't compromise on it. And I don't mean superficial stuff like a ping pong table in the break room. I've been told I'm idealistic, perhaps unrealistically, for wanting to work on cool projects with cool people. And yet I ended up doing just that, because I didn't waste my time considering jobs that didn't have those two things. (Same goes for dating too.

)
But again, often not possible for someone if they haven't considered Tip #1.
Hope this advice helps someone, even y'alls can be really cynical sometimes.
