Mistake #1. Having no social media strategy. Randomly posting without a reason is only a little better than not posting at all. In order to get the most out of social media promotion, you have to have a strategy about your goals and how you're going to accomplish them.
Mistake #2. Creating accounts on too many platforms too soon. No one can be on everything and do them all well. Pick one and get good at it, then add another, etc. Choose the social networks most used by your fans or potential fans.
Mistake #3. Paying for fake followers. Those follower or viewer counts sure look good when they climb overnight, but your real followers won't be fooled and neither will record companies, management, agents or anyone else in the business. Get your followers the old fashioned way - earn them with great content.
Mistake #4. Talking about nothing but yourself. You're using social media as a promotional tool but your posts get boring if it's all about you, your band or your music. Talk about your followers, ask questions, throw in some relevant news and generally change it up to keep the interest and engagement high.
Mistake #5. Using irrelevant and excessive hashtags. Hashtags that don't mean anything are useless for promotion. Using more than two on a Twitter post (more for Instagram) actually decreases engagement, so choose them carefully.
Mistake #6. Sharing too much in a short amount of time. Dominating a feed is a great way to lose followers. If you're going to post a lot in a short period, at least warn your followers beforehand.
Mistake #7. Forgetting to proofread. People judge you by your grammar and spelling. Check it first before posting.
Mistake #8. Neglecting the “social” aspect of social media. Remember that engagement goes both ways. Be prepared to respond to comments or questions on any post.
If you're not sure how to develop a social media strategy, or want more information on using social media as a promotional tool, check out my book Social Media Promotion for Musicians. You can read some excerpts here.