So I figured I'd try to help people out and offer some advice on some aspects of writing as a career, since I've technically been doing it for a few years now. (With, uh, varying amounts of success.)
Let's start with cover art, because as much as people FUCKING LOVE to say, "Don't judge a book by its cover!", they do. Pretty much everyone does.
However, I do want to emphasize that the real foundation of your career as a writer is the writing itself. You need a solid core, a firm foundation of quality writing with which to build on. Otherwise you probably won't get anywhere.
(Not trying to come off as sound liking some elitist bitch. I don't think I'm great at writing or anything, I just try my best and hope people like it, and practice pretty much every day.)
So, cover art.
First thing's first, you need to determine whether or not you have an eye for visual art. This is...admittedly hard to determine. I'd recommend just trying to make some covers and see where you land. Either you're abysmal and come to realize it's going to take a LOT more practice and research, or you might not be half-bad at it, or you're a natural.
From there, you should determine whether or not you want to put in the work. I can understand why you might not want to. It's the exact reason why, as soon as I got some money, I began working with someone to help me. Cause I suck at making cover art.
If you are looking to go it alone, here's some resources.
PIXABAY. This place is nice. It's basically just a massive collection of royalty free images you can use. I'd recommend getting an account, just so that you can download the biggest versions of pictures. It's no-bullshit, no hassle as far as I can tell. I haven't had any kind of trouble and I've had an account for awhile now. Go looking through this for images that you might want to use for your cover art. There's a ton of stuff on here, but most of it isn't amazing. There are some hidden gems though. Basically, try typing in a lot of different phrases if you're looking for something specific, because different words can bring up totally different results.
SHUTTERSTOCK. It's kinda like the pro version of Pixabay, in that it costs money. The images aren't super expensive. Individually, anyway. The pain in the ass is that you can't just buy one image. You have to buy, like, credits or something, in packs, and then use those credits to buy pictures. It isn't really a scam or anything, as far as I can tell. Once you jump through the extra hoops, you can buy the images without a problem. It's just a psychological trick they use to try and get you to spend more money. The bigger the amount of money you spend, the cheaper the individual pics are. They REALLY want you to sign up for a monthly subscription. If you want to buy just like a few pictures, it's fucking expensive. If you're invested in making covers for yourself, and you produce a lot of content, this is probably worth investing it.
GIMP. Sounds kinky, right? It's actually not. Basically, this is a free, open-source photo editing program. It is...complex. Or maybe I'm just an idiot, but it took me awhile to get the hang of it, and even now I realize that I'm only utilizing maybe 15% of its total abilities. It has a LOT of things you can do to make pictures, but it will take a bit to figure out. If you're looking for a given effect, google it. There's probably a reasonable tutorial on how to do it. If you're serious about making cover art, this is worth investing time into.
There's a lot of other stuff out there, but this will get you started. Also, IMPORTANT NOTE! If you are writing erotica and are going to use someone's picture, like a model you got from one of those sites, don't use their face! Not unless you got it from a site that's specifically okay with using models for that purpose. I doubt there exist vast AIs or bots trawling the internet, looking for erotica that uses some people's faces on the cover art, but it's just not worth the hassle if it ever does come up. Some people get really touchy with this and it's basically their legal right, I believe, to say that you can't use their face on your sexual content. I mean, as far as I know. I'm just a cautious person out of nature, so I don't bother.
Now, some general advice on making cover art.
No Crowding. Try not to put too much stuff on your cover, specifically text. Really, the most we need is the title and the author's name, and perhaps a byline (basically one of those little taglines you see on the covers), or maybe (MAYBE) a piece of a glowing review, if you somehow managed to get someone with a big name to publicly review your book.
Eye-Catching. Try to make your cover have some kind of central image or maybe a good color scheme to make it eye-catching. Something that snags your attention the second it enters your field of vision. Obviously different things attract different people, and this is more of an art than a science. Honestly though, like a lot of cleavage works well, I've heard.
Centered Text. It is your friend and it looks pro. Center your name, center the title. Unless you've got a stylistic reason to do otherwise, which plenty of people do. But it's gotta look good otherwise.
Series/Brand Recognition. If you're going to do a series of stories, they all have to resemble each other, to let the reader know that it's part of a series. Or, if you're going really big, it's part of a brand. Your brand. This can be super hard. For a long time I used pink silhouettes and I...have no idea if that worked or not. But I do know that not a lot of other people were using silhouettes, so hopefully it gave me a bit of good branding. Maybe go with a very specific font, (oh yeah, check out 1001fonts for some cool fonts, but make sure they're free to use and not licensed, or you'll get in trouble, but if you find one you really like, you can place it right into GIMP.) Or maybe create a little logo that you put on every cover.
Thumbnail. Whatever you make, it has to look good as a thumbnail. You know how the covers are small when you're browsing in the Amazon store? Basically that. It should still look good and be recognizable and legible at that size.
Now, what about if you don't want to make your own cover art?
Well, luckily there's some places you can go to get relatively cheap cover art made if you're strapped for cash.
First thing you'll need is a paypal account. Pretty much everyone operates on them and they aren't too much of a hassle.
I used fiverr for awhile. I recommend signing up and then go hunting for top-rated people making cover art. You'll be able to at least get decent cover art for cheap, either 5$ or 10$ usually. I used this person for a long time. She charges 10$ a pop now but if you aren't getting a crapload of works like I used to (I needed about 9 per month), then you should be fine. She's fast and reliable and pretty good at what she does.
Now, I found the two people that I currently now work with through the website artistsnclients. This is basically a site that hooks you up with people who draw, if that's what you're looking for.
You might also want to check out deviantart. I admittedly don't really know about about it, but some cursory research led me to believe that some artists might be open for commission. Find something that you like and maybe PM the artist and ask if they'd be willing to let you use it, or maybe to commission them to create something like it.
ADVICE: If you are going to go to someone to create a drawing or something in-depth, I'd recommend being up front about the fact that you are going to use this as cover art. Tell them this right from the outset, because I think it's fair to let them know whether this is something for your personal collection or something that's going to be part of a commercial endeavor.
There's certain a hell of a lot more to making cover art and even having cover art created for you, but I think this about covers the basics.
Hopefully this helps someone.