Here's some of my advice on how to find art jobs: (sorry if you know some of this already)
Online Job PostingsMost of the sites I used to look for jobs on are gone now, unfortunately, but you could try these:
http://www.conceptart.org/go/artjobs/ - Not terribly active anymore, but still worth checking periodically I think.
https://forum.deviantart.com/jobs/offers/ - Extremely active, mostly anime, and a lot of very low-priced stuff, but there's some serious things there too (with more competition of course). I never used it myself, but it may be a good place to start.
https://www.reddit.com/r/hireanartist/ - I've never used reddit either, but this looks like it could be useful.
You have to be careful (and wade through a lot of poop job listings) working with random online people, but I've found some great recurring clients that way
"Cold-call" EmailsYou can also email your portfolio link directly to game companies. Just write a short message saying you're looking for work, a past client list (if any notable), and a link to your portfolio (Artstation or a well-designed personal website). No need to blather on about how much you would love working for them (or vice versa), they know what you're after. Small tabletop game companies are a good place to start, the smaller the better. They hire out tons of art but don't have huge budgets, so the competition isn't too fierce (and some of them actually pay quite well for the time and lesser hassle required). Most companies have contact info for freelance art submissions on their websites. A good way to find companies is to look at artists' websites: often they have a list of people they've worked for. Or you can search around for products and see who makes them: board games, card games, tabletop RPGs, miniatures, etc.
CompetitionExpect plenty of competition. Online job postings often get a few hundred responses, especially if they mention any amount of money. Companies also get lots of emails from people just like you. Don't waste your time obsessively checking your email/messages.
Look for jobs, apply to the interesting ones, and forget about it. Most of the time you will not get a response. Don't get discouraged either, just keep improving your art and applying to jobs. You never know what people are really looking for (they probably don't know either).
Contracts & PaymentThere's no good reason to work without a contract. If the job is for a company then it's easy: they will send you a contract to sign. If you're working for a random person then it's a good opportunity to have your own simple contract handy. You can grab
this pdf pack on Gumroad (it's free), it includes a sort of template contract that you can adapt. I'm sure you can find other templates too. (If you're really interested, PM me and I'll see what contracts I have lying around.) You (and your client) can sign things with Adobe Acrobat Reader. Just click on the "Tools" tab and find "Fill & Sign".
You
can work without a contract, and it may be fine, but let me tell you, it feels bad when someone rips you off and never pays you. Contracts help keep people honest. If a client gives you grief about signing or just avoids talking about a contract, drop them. Just say you don't think it will work out after all and run away. Likewise, if you ask them how they plan to pay you and they don't answer, be
very suspicious. Maybe they just forgot that question; ask it again. If they keep being cagey about it, drop them. For payment I've basically always used Paypal, except for a few US clients that will mail me a check.