Tell people that you are on twitter. Put a link in your newsletter, on your facebook, on your YouTube channel or even better import your email contacts into twitter.
Make sure what you tweet is great. Put thought into filling those 140 characters.
Ask your followers to retweet your important posts.
Use hashtags but not too many. Too many hashtags looks a bit needy.
Don't be afraid to retweet others. Twitter is all about sharing.
Put your twitter link in your email footer.
If something is trending then get involved.
Follow people relevant to your niche.
Add a tweet button to your blog.
Give #ff Follow Friday a go