Anyone who is self-aware and thus would be <i>interested</i> answer your question, would have worked on removing these habits and thus not have the <i>answer</i>.<p>I can answer what my worst habit was previously: watching TV. TV shows and video games are designed to be very compelling (read: addictive), and removing TV and games completely from life has given me so much time back.
Embarking on a task, realizing that it requires more foundational work than I'd anticipated, and plowing ahead regardless in an attempt to finish it all in one go. It nearly always leads to frustration and lousy code. Then I have to back off and break it down properly into manageable chunks.