The worst kind of bad habit is the one we can't get rid of, no matter how hard we try. The worst kind of bad habit is also the one we don't even try to break, but instead we allow it to continue without any real opposition.
But most of all, the worst kind of bad habit is the one we refuse to turn over to God. We may try to fight it on our own, or we may simply give up trying, but we never acknowledge our own helplessness and turn to God for the strength we need. Perhaps we think He doesn't care about us, or that He won't help us. Or we may even be driven by our pride, refusing to admit we need God. The Bible warns, "Do you see a man wise in his own eyes? There is more hope for a fool than for him" (Proverbs 26:12).
This is why the first step is to turn your bad habits over to God and ask Him to help you overcome them. You have trusted Christ for your salvation; now trust Him to help you every day. When temptation comes, learn to turn immediately to God and ask Him to help you.
Take practical steps also; if you know you will be more likely to yield to temptation in certain situations or around certain people, then avoid them. The Bible says, "Do not be misled: 'Bad company corrupts good character'" (1 Corinthians 15:33). Above all, make it your goal to grow closer to Christ. The closer we are to Him, the less Satan can touch us.