Know your target audience, as an author I have spent many hours in boring webinars learning how to publicise my books using social media and other similar methods. Lots of people think they can post a product they have made whether it be a 3D model or a cats waistcoat on their personal Facebook, Twitter, Pinterest etc. and it will sell by the tonne. Not true. If used badly, social media is as much use as a chocolate teapot.
1. Know your product
2. Know your customers
3. Know where your customers go.
Example; If you make game-ready models, you know that the target is game-devs/ advertisers (and a few others). Your Auntie Joan might like your model on Facebook but she sure as hell isn't going to buy it! Join game-dev groups and post your model there CAREFULLY. Don't get kicked out of the group for spamming.
Join Reddit groups that are concerned with your "theme" of the model(s) and answer a few posts before wading in with "Look at this I made, now buy it".
A blog is also a pretty good way to sell your stuff and also a Youtube channel. My blog gets around 1200 or so hits a week because I don't spam my models, I do spam my blog because I can get away with a link in every post more than I can a massive screenshot.
I don't post a lot on social media but when I do, I tag appropriate bots that will repost my links to a lot more people that follow me.
Good luck.