The most important part of hanging a shingle is keeping costs down. As a starting solo, you only need 3 things: (1) cell phone, (2) business cards, (3) suit. You don't even need a computer - you can use one at the library. (that being said, a computer and a good printer should be the very first 'luxuries' you buy when you have some spare cash).
Even an office is unnecessary* - you can meet clients at their place of work, at their home, at a cafe/restaurant/coffee shop.
Solos can be successful in almost any field, but corporate is much harder to break into - especially M&A and securities. If you have an interest in a specific field, go for it. If you're not sure, just take whatever clients you find in the beginning, until you get into a groove. In the long term, you don't want to take anything that comes over the threshold, because you won't be that good, and you won't make as much money as people who specialize (because it takes you longer to do the same work, and probably at a lower quality).
The most common fields for solos are:
Bankruptcy / Consumer Debt
Labor & Employment
Trusts & Estates
The great thing about Crim, Divorce, and Immigration, is that if you do a good job, you'll quickly get referrals. Criminals tend to know other criminals, immigrants tend to know other immigrants. Likewise, anyone getting divorced is likely to be put in touch with a friend-of-a-friend who also got divorced and can recommend a good lawyer.
Bankruptcy and Disability tend to be volume driven - the profit per case is very low, but the work is fairly simple. These practice areas are very much driven by effective advertising
Personal Injury requires deep pockets - not only does it require effective advertising, most of the work is contingent, you're covering various fees, and possibly paying for experts. It gets expensive, but the payout can be huge
Real Estate is volume driven. But if you can get some realtors to send you their clients, you can have a steady stream of repeat business quickly.
T&E is arguably (and IMO) the hardest field to break into, but also the best lifestyle - done right, it's low-stress and you can set your own hours. It takes forever to cultivate steady referral sources, and advertising is expensive, but if you have the cash, you'll get there. There are also a lot of networks that are more than happy to help you, for the right fee. Note: stick to the simpler stuff. Any idiot can put together a basic will, but reducing someone's taxable estate by transferring assets on a discounted valuation can be quite tricky even for people who do these things regularly.
I also recommend considering new areas of the law that more established firms may shy away from. During the past decade, Cannabis and Crypto were good fields to break into. Both areas are now more mature and harder to break into, but at the time there was very little competition,
The hardest part is getting started. It could take a while before you get your first client, and much longer before you get in a groove where you're regularly generating business. And it takes a while to really start earning. Everyone I know (admittedly, not that many) who went solo in a major city made between $20k and $50k in their first year, with $35-$40k being typical. It's pretty low, but it should grow pretty steadily. Eventually, it'll be worthwhile (and not just the money)