http://www.socialmediaexaminer.com/twitter-tactics-to-increase-engagement/
#1: Keep Tweets Under 110 Characters
#2: Tweet During Daytime Hours
#3: Tweet on Saturday and Sunday
#4: Share Images
#5: Ask for Retweets
#6: Use Hashtags
#7: Include Links
#8: Stay Away From Lifestyle Tweets
#9: Use Strong Calls to Action
#10: Send One to Four Tweets a Day