If you have problems keeping your tweets up-to-date and in a constant stream, consider using programs where they can be stored, and "uploaded" according to a schedule. You will be able to write a tweet and release it multiple times, on relevant dates – such as holidays and events.
Make sure you use a software product that informs you when you receive direct messages and @ mentions. Being active and responsive will help you attract and maintain users. If users think that you're just spouting sales material for self-promotion, they won't stay followers for long.
Make sure you proofread every tweet you make. It might seem trivial, but making sure that tweets use good grammar and have no spelling mistakes, will make you seem more professional, and your tweets will be more readable. If your followers are having a hard time understanding you, they won't stay with you for long.
4) Followers' expectations
If you are famous for a certain type of product or occupation, your followers expect you to dispense knowledge or quips regarding it. If those types of updates are scarce or nonexistent, the number of followers you have will slowly reduce, and it'll be hard getting them back.
You need to make sure that the amount of self-created updates is high enough. Don't just post a joke you just heard, that everyone else already knows. Your followers are looking for something new, preferably something that is related to you – either personally or by occupation