Read the book, Atomic Habits by James Clear
What are you doing you wish you weren't doing? Think about what you're doing on each side of the habit loop. What are you doing right before the undesirable behavior and right after? Change those and you'll change the behavior
Treat yourself like a scientific experiment, watch yourself and notice your habits.
Replace old habits with new ones. Change up your activities surrounding your habits.
When and where do you practice unhealthy habits? Are there certain friends or activities that elicit unhealthy behavior? Change your pattern (walk a different route to get out the door if cake is in the kitchen at work)
Pair a difficult to remember habit (wearing rubber bands with braces) with something you already do all the time/an existing habit (reaching into pockets)
Think about how a new habit will make you feel (making the bed in the mornings will set the tone for the rest of the day). If you're doing the habit because you desire a feeling, this is more likely to stick than doing a new habit just because you think you "should" make your bed.
Trick your mind by saying, "I'm the kind of person who... (insert desirable behavior)". This plants the idea into your head which will change your choices eventually. For example, if you tell yourself over and over, "I'm the kind of person who makes healthy choices for her body" you'll eventually believe it and make choices to reflect this statement.
You can also say, "I'm not the kind of person who (eats standing up)." If you're not that kind of person, how would this look?