SOME BASIC TIPS:
Quality of promotional material and the game itself is #1. The game has to look good enough to persuade buyers to download or buy, and then actually be good.
Graphics are important to a lot of people, and visual interest is crucial to making any sales.
Not that it needs to be photoreal or anything, it can be pixel art or very stylized, but there must be appeal there, and a certain stylistic consistency that is effective in communicating the game's play. Some titles have done will with very simple graphics (eg. Baba is You) because they had a creative concept in game design, and that is important too, but it is the visual look of the game that will offer a first impression, and the gameplay that follows will be the retention factor post purchase that makes the game spread via word of mouth. But to manage the first few purchases, you need to make the players interested in playing, which usually will be an uphill battle if the game doesn't look interesting visually. Pricing is also a challenge - even a single dollar of price is a psychological barrier for many people so as others have stated, demos help in letting people try the thing and see that it runs and is fun, and once they've gotten to the point where they like that demo they are likely to buy the full thing. The less friction is involved in that upgrade the better - it's best if the free demo includes an easy link back to the page where the full version can be bought!
Visibility. That is letting people know your work exists. Social media is one avenue but if you're posting on a single social platform and not multiple that's not great, and you need to engage with communities interested in the type of thing you are doing. [Related gaming fanbases for your genre] and create links back to your game as you do so. Think about visual media as images will grab attention faster than text, and animation even better still. Pinterest, Instagram are social platforms focused on visual media and they can be worth using. Also, as stated earlier, sending info of your game to relevant streamers/YouTubers who play indie games is good but don't expect more than 5-10% best case to respond. It is not enough to message one or two people, you've got to have a whole list of YT people to message and also maybe some game review sites, gaming blogs. This will of course work best if your game's good! Also, a trailer (YouTube video, 90 seconds or so) highlighting the game is a good move. It should show the game's look and play, it should sound good too, and get across the appeal of it without needing to cover absolutely everything that is there. It should have a note on where and when the game is releasing - on the end screen. That leaves interested people with some indication of what to do next. A big link in the description back to the Steam page, game website is best. (You ought to have a webpage and domain for it ideally)
Accessibility. 80% of PC game purchases roughly are on Steam. If you're serious about reaching players and racking up sales on a game you made that actually is of quality, SERIOUSLY consider Steam as a venue. The $100 entry price is a challenge but also may be worth it if you believe the game is not a little personal experiment but an actual potential success that can sell dozens, hundreds, even thousands of copies. That will - again - only happen if it's fairly good.
But if you have one flagship title and can get it onto Steam, its revenue may be enough to pay the fees for all the subsequent stuff made after that. Seeing as in most genres on Steam the median sales value is $1000-7000. That is, if you can be in the middle of the pack in quality and interest, you'll be netting a thousand dollars or more there. My target on many of my projects is be slightly above the average in quality with a specific quirk of aesthetics or structure that sets my game apart from the genre and subgenre it's part of. And if I am there and I make $2000 per game that's about the threshold where it's worth it. As that is about how much I spent on the average game of mine, so at least there I'm not losing money. Some titles with handmade visuals are the most expensive ones of mine. Miniature Minigolf {Minigolf courses all done in mini with stop-motion, etc), Miniature Multiverse (Myst-like first person puzzler set in a mass of fairly large scale miniature environments carefully handcrafted) and sometimes I've hired people to solve specific weak spots - a coder to figure out a particularly difficult code interaction, a couple of musicians who composed music tracks...) A lot of this is funded by revenue from my Etsy shop which is way more successful than anything I've done on itch.io. (I sell original art and print services and papercraft designs on Etsy)
WHY SHOULD ANYONE LISTEN TO ME?:
I actually am taking this seriously and working hard on a handful of indie titles (various game dev projects with varying but appealing art styles from hand drawn to miniature art and painterly, 3d and 2d... ) and I've yet to release a lot of what is in the works but I have netted $200+ in sales on itch all the same simply selling game asset packs. There are 3000+ asset files available across a bunch of different collections on my itch.io profile, likely 5000+ will be there by end of year. The range of stuff all just keeps expanding as I keep going on it. Mostly textures (seamless, photography-based PBR texture packs built from real-world sources and materials I photographed myself) and 3d assets (models efficiently UV mapped, collections of them with low polycount, but reasonable levels of realism and in .FBX, .OBJ formats that are widely used.)
There's no shortcut to success here as with most things. It takes a ton of time and skill and persistence. Indie dev is not a 'quick buck' thing but takes a long time to build to the point where your work is so solid and intriguing and compelling that people actually want to buy it. Most of the hobbyists who try will fail but those who are driven primarily by creative passion and the process and a desire to actually offer value to the gaming and game dev community and not simply rip them off, are the ones who will persevere and work hard and long enough to end up making things that do, ultimately, eventually succeed.