1) Be real and be yourself. No one likes a promoter who just does that and nothing else. "Attraction not promotion". Have an attractive set of Tweets and people will naturally be interested in what you are "selling" and/or who you are. Sometimes I will go back to clean up my Twitter to delete tweets that are conversational so as to keep my timeline "attractive" to new people. I want them to understand my feed as opposed to reading one side of a conversation. Usually after I follow a bunch of people I will go back and delete some tweets and clean up my timeline so it looks sleek and easy to read and digest.
2) RT RT RT : ReTweeting is a way to be reciprocal on Twitter. It shows that you are not one-sided and have interests other than yourself. It is the Twitter version of "feeling like you are being heard/listened to." By RTing others you are engaging with them in the most basic way by saying, I agree with what you said and I want to share it with others as well. It is the email version of a "forward".
3) Do NOT care who unfollows you (unless it is your best friend). There are millions of people who are not following you already. Why focus on the negative? It will not help. And please do not post about who is unfollowing you, etc. Nobody cares. It is only showing your insecurities on your timeline. We do not need to see that.
4) A good timeline is a combination of interesting personal tweets, RTs, conversation, and links to interesting content. Strive for a balance. When people are considering to follow you, it makes for a rich twitter page.
5) Reach out, ask questions, give answers and actually care. These are real people (minus the 80% spam) and you should be treating Twitter as an amazing city block in which you live. All sorts of great people and opportunities are available to you, just a click away.
Please feel free to contact me with any questions about the Twitterverse.