I'll tell you what I've done to prepare for private practice. Since I am most familiar with criminal defense, I shall continue to pursue criminal defense in the private world. Thankfully, since criminal defense is constitutionally mandated, many opportunities are available. There are a variety of panels, for instance. In most counties, there are panels of attorneys who handle conflict cases; cases that the public defender has a conflict with. There are also sometimes panels for 2nd or even 3rd level conflicts. There are panels for appeals work. And there are panels who handle parole work. One thing you should know is that each county organizes the panel differently, so you should find a local attorney to work out how one applies for panel work. For example, in El Dorado County, there is a panel of a handful of independent contractor attorneys handing conflict cases for a set amount of money per year. In Placer County, there is a private conflict firm who handles conflict cases for a set yearly rate. In Sacramento County, there is a loosely organized panel of independent attorneys who earn as they go, but there is no apparent limitation of panel membership. So, as you can see, it takes research.
My county is like the third; a loosely organized panel of independent contractors with no membership limitation. I am told that it will be enough to get by while I build the private portion of my practice. Of course, I am lucky because I do not have any immediate financial concerns, such as dependents or immediately due debts (other than college loans). However, even if I did, I would want to get on the panel immediately.
Be forewarned: getting on any panel takes time, no matter where you go, so plan accordingly. Knowing this, I applied for the panel long before I quit my job, and even then the transition has NOT been seemless. There are always hidden requirements that one must have in place before taking cases. For example, I was told that I have to watch a "few" training videos before I can start taking cases. I thought a weekend of video watching. It turned out to be 48 solid hours of videos. And you can't watch them 24 hours a day at home; you have to watch them at the panel offices so they can be sure that you watched them. Hmph.
Also, getting a quote on malpractice insurance is a surprisingly long process. I erroneously thought it would take a day or two to get one. Oh no. It took two weeks just to get a quote. Check with a number of different lenders because rates may vary dramatically. A little patience will pay dividends. I was able to save hundreds of dollars as a result. You will find, though, that they are completely unsympathetic to the need to get a quote immediately. You will just wait, maybe longer.
Office space is often a requirement to take panel work. Initially, I had hoped to work from home and rent access to a conference room from time to time. The panel requires an office address. I assume you can find someone who will share space with you, but in the admittedly poor research I've done, it is often more pricey than getting your own tiny office. The reason for that is they often want you to pay for a portion of their overhead as well, which is something you must avoid at all costs and probably don't need. Thanks to the market downturn, I found a place with a reasonable rate close to court. And, moreover, it is slowly becoming my manspace, which is indeed a benefit when you have moved in with your girlfriend, as I have done.
The real problem, at this point, is that I'm spending my entire day trying to comply with the panel requirements. As a result, I am unable to take private cases. And, thanks to previous contacts, I have some potential cases coming in that I just don't have time to take right now. This video watching has seriously consumed an entire week and half, not to mention the problem with finding office space, furniture, and insurance.
A note on furniture: I am a person who cannot take shitty partical board furniture any more. It costs a lot and does NOT last. I know this because I have spent my career in public defender offices dealing with this crap. Fortunately, I had saved enough money to get a nice desk and I've had a donated bookcase and table. The point I'm making here is that decent, well-made furniture is not as readily availabe as you might think. I have spent substantial hours trying to find real wood furniture. I tried going to a furniture store and asked where the non-particle board stuff is at, and they told me they can get it by ordering it only. And this was a giant store. There's some good stuff out there, you just have to spend a substantial amount of time looking for it.
So, I am nearing the end of my video watching. Hopefully, once this is done in the next day or two, I will begin taking cases. At which time, I hope I can describe the process.