Personally, Instagram is better for posting art since the quality for pictures in twitter kinda suck. However a lot of people from tumblr migrated to twitter so it would be better to know your audience.
First, you need to be respectful of everyone and everything unless it's problematic since twitter users LOVES to drag people by quote-RTing causing people to attack the initial poster.
Second, avoid quote-RTing artist's art. Most artists finds that disrespectful since it takes away the likes and retweets from the original post. Do reply/comment as you wish tho.
Third, focus on finding like-minded people first because twitter is all about interactions and you would need people/friends to RT your work to gain traction. Tags are sometimes useful but successful twitter users that I've seen usually relies on wit/humor or mainstream fan art to gain traction. Else just be mutuals with popular twitter users.