Research has shown that any given habit becomes more automatic with more practice. On average, it takes at least two months for new habits to become automatic behaviors.
You should focus entirely on one habit. Research has found that implementation intentions do not work if you try to improve multiple habits at the same time.
You are 2x to 3x more likely to follow through with a habit if you make a specific plan for when, where, and how you are going to implement it. This is known as an implementation intention.