Finally, some last notes and tips.
Check out ThatMerchantGuy on Twitter. He shares a lot of art, and is even working with Japanese artists for getting new art done. He's great.
Pixiv almost always has the best quality. Run art through saucenao if you want to check to see if it's on Pixiv. Many Twitter users also have a Pixiv account. However, they may not upload everything to Pixiv. It's best to regularly check both of these, as they're the primary hubs for art.
When using Twitter, make sure your URL has :orig at the end. That means it's the best size and quality. You may have to delete the :orig off the filename when you save it, or your computer won't recognize it as an image filename extension.
Tumblr is usually worse than Twitter because they limit the dimensions of photos. However, artists also often post PNG photos, which are higher quality, on Tumblr instead of Twitter. The magic number for Tumblr is 1280. If you can't get your image past a 1280 size by setting the URL to 1280, it's been scaled down. Exercise judgement in whether you want a picture with better quality or better dimensions when choosing between Twitter or Tumblr. The choice is up to you!
I don't search for many tags on Tumblr because art quality varies and the site is difficult to use. To make up for this, I try to check archives on users. That way, I can find their old art and art that they liked.
Instagram is also limited in image size like Tumblr, but its photos are also generally of a lesser quality. You should try to see if an Instagram artist is on another site. Even so, some only use Instagram. In that case, just enjoy the photo, and don't worry about its quality. Also, most posts on Instagram will be Ann cosplay, not art.