Say, in your case, you plan to give up negative thinking, which is extremely hard (if you tell yourself to never think of purple flying monkeys... in other words, controlling your thoughts is hard) and self-destructive behaviors (moderate level of difficulty, since controlling behaviors is easier than controlling thoughts).

so if you take the tiered approach from Eastern Orthodoxy, which has been in development for centuries and must have some rational basis under it, you may plan to first give up behaviors and only later, negative thoughts. And, I really like how someone suggested not just giving up negative thoughts but substituting with positive ones.

With all that, controlling thoughts is still so much harder than controlling what fats are used for cooking, so give yourself a break!