I'm in this process now, so I can cover what I've been going through.
First you need to outlay what your reasons are for living aboard. Do you just like marinas and what to live on a barge at a dock? Do you want to sail around the world? Do you want the ability to pick up and instantly move elsewhere but don't plan on extended cruises? Do you want to spend your weekends anchored out and the week at the dock so you can commute to work?
If you lay down how you want to live, that sets a groundwork for a budget. For me, I want to be able to work part of a year, save up and then spend the other part out cruising. The less money I owe to a bank the more time I can spend away from dock, so I want a boat I can pay off sooner rather than later.
Next you need to realistically assess your lifestyle needs. Right now, when you get home from a hard day's work if you like to crash back on the couch, crack open a cold beer and watch the game, then a boat lifestyle that supports that will probably be more successful. How much stuff will you be taking with you? Are you cool with getting out of your boat at 6am in sub zero weather to take a shower? If that sounds miserable, maybe find a boat with a separate shower stall. You gotta be realistic in your needs. Less is more, you're gonna have to give up some things, but you also can't be miserable.
Personally I'm finding the above two things to be really creating a balancing act of "What boat do I want". I want to go big enough to meet MY unique needs of comfort and livability, but anymore than that and I'm delaying my ability to start my lifestyle dream of breaking away from land for long periods of cruising.
Once you get that down, it gets easier. Read up on everything, look at boats to make sure they'll suit you, save up for the up front costs, understand how much you'll need to put away each month for boat maintenance, visit marinas to see if you'd want to live there, talk to insurance and financing companies... then do it