What makes a good Tweet? Here are several factors that I've found from across the web that can influence engagement and increase your followers.
1 - Hashtags
1-2 hashtags at the end of a tweet gain more engagement than when mixed in with a tweet
But using hashtags mid-sentence? That’s primarily a historical artifact of how hashtags were once used - Christopher Mims
2 - Images
Tweets with photo's lead to an average of 35% more engagement
Photos average a 35% boost in Retweets - Twitter Blog
3 - Length
The optimal length for a tweet is 70-100 characters
Tweets with more than 100 characters receive 17% less engagement than tweets with between 70 and 100 characters - Buddy Media
4 - @
Starting with an '@' is semi-private when you want to be seen, begin with anything but @
When you start your message with @someone, the message will only be sent to @someone and the people that follow both you and @someone. - Dave Larson/TweetSmarter
5 - Emoji's
They are a necessary part of digital communication. Use sparingly and in context. They can be misinterpreted so be careful when using Emojis.
Emoji's take the place of the facial expressions we'd use to measure meaning in the in-person conversations - Tessa Wegert/ClickZ