I have SO MUCH advice! These are based off my experience as a freelance commission artist for over 10 years, but do whatever works best for you!
Communication: I insist clients email me for a few reasons. First, it gets really confusing if you tell clients to DM you, then they message you on twitter one idea, DM you about a change on Discord, then ping you on Instagram for an update. It's easy to forget which client told you what, and where. Insist on having ONE place clients contact you. I use email because they are more formal than DMs. People put more effort into their replies than they do in DMs, where you can also lose track of commission info by chatting. If you email, you have clear records of the conversation, which could also be used in case the client wants a refund or does a chargeback. Emails can't be edited or deleted.
Presentation: I recommend creating a website for free on wix.com to showcase your commissions. It's easy to use and they have lots of free customization. Include a gallery of your work, your prices, and your commission info with Terms of Service. (SUPER IMPORTANT YOU HAVE ToS AND MAKE SURE CLIENTS AGREE TO IT. You can use mine as reference if you want!) If making a website will take too much time, a public Google Doc with your prices, commission info, and terms of service would do fine. But have a portfolio of your past work for clients to see: you can use Instagram, Artstation, DeviantArt... anything with an easy to scroll through gallery. Clients need to be able to see your work so they have accurate expectations of your ability.
Recognition: If you're just starting out and find that no orders are coming in for your commissions, there's two things you can do. Practice and Advertise. Maybe it takes you 6 hours to draw a chibi, while it takes other artists 2, and if you charge $65 to their $25, you think you need to undervalue your time to meet demand. But that artist has their own following for people who want to commission them, you need to make your own following and get paid fairly. So you can Practice and work on your skill, speed, style, and draw things you're passionate about! Personal projects always shine brightly cuz we know what's great about the thing we're drawing and it helps us make good choices. If you don't have clients, draw for yourself or to learn. Work on your craft, and make cool stuff others will want to order from you too! I just did a sketch of one of my D&D characters, her outfits, and the equipment in her bag for fun, and now I have people wanting to commission me for something like that. So if you don't have clients, practice and make cool stuff to show off! (Practicing will also increase your speed and you might be able to draw that chibi in 2 hours yourself someday.) Showing off ties into Advertising: which is all about building your brand and a community. Post to social media whenever you complete something: Twitter, Instagram, ArtStation, etc... and respond to the community there! Building relationships is a great way to grow in any business. Another good advertising tactic is Giveaways: if you have time, do a giveaway on Twitter for some free art! Ask people to follow you and retweet to enter. It'll raise your follower number, spread your content through the retweets, and get more eyes on your work that could lead to paid commissions!
Prices: When you're starting out I suggest you charge at least minimum wage per hour of work a project takes you, and fluff it a bit for taxes and PayPal fees. Estimating cost is tricky cuz you have to do it ahead of time: but ALWAYS have the client pay 100% upfront. I've had clients ghost me, come up with every excuse why they couldn't pay, promise to pay later but don't, and by then you've already done the work. I send progress updates and like to offer partial refunds so clients can actually back out if they don't like the sketch or my design or anything. But usually once people have paid they're willing to work with you on edits. You can offer some edits for free, or charge your hourly rate for edits. Then once you have more renown, increase your prices to meet demand! If you're getting more requests than you can handle, raise the price to something that has less people ordering but still enough to keep you busy.
Edits: I offer sketches and progress edits to my clients. If you jump straight to delivering the final artwork, chances are they'll wish something was different. They may ask you to change it, and changes are hard to make when you've already polished the finished piece. Sketches are meant to choose a general, messy concept of a piece to make sure the client and I are on the same page. It's easiest to change at this stage, so clients can correct me if my vision of their piece is wrong, and I won't have lost a lot of work. Then I offer a progress edit when a piece has only it's linework and flat colors (no shading). At this point I ask if clients want to edit things like colors, or correct small elements. If they ask for a big change that's completely different from the sketch, or ask me to change the same thing more than twice, I might charge my hourly rate for edits. But it really helps with client satisfaction if you ask for their feedback! Don't be afraid to ask for visual references if the client isn't being clear about what they want.
Delivery: Be sure you can dedicate the time to working on a commission once you have recieved payment. Give the client an estimate for how long the project will take you, but double it for safety. Then you have extra time if something goes wrong, but delivering early always looks good. I try to keep clients updated weekly on the state of their commission, even if nothing has been done, just to let them know I haven't forgotten about them. If something arises, let the client know! People are usually understanding, especially if you're proactive and reach out before they have to ask you for an update.
My final tip: Know your worth. Be polite and professional, but don't let anyone take advantage of you. If you worked out fair pricing, stand by that. You deserve to be paid for your time, your experience, and to meet your demand. If anyone tries to tell you otherwise, they're not a client you want to work with anyways. Exposure will only get you exposure to other people who want you to work for free.