I don't tweet unnecessary things. So whenever I find something important to share I tweet on Twitter. The average number is highest twice a day.
I tweet about relevant articles to my niche I read each day and thats usually 2-3 tweets throughout the day and then whenever I write up something useful for my followers I will tweet it in there on top of others during the day. That allows me to provide them with relevant sources and then have enough community involvement to be able to post promotional stuff whenever I have something.