Habits are built on many emotions, skills and measurements, like time, patience, consistency, sacrifice and even rewards too.

Some of them might even go together. For example, you might have to sacrifice time on one thing, for another, if you don't have time for both

Start by identifying your goals, what's important to you and your personality plays a big part in this as well.  This will give you the platform for building and breaking habits. so now that I've established what my goals are, I can establish what I would need to achieve those goals.  and to achieve these specific goals, I would need to do XYZ.  x y and z would, of course, be habits that you would need to learn for the benefit of your goals. Daily exercise could be considered an excellent habit to have when you have fitness goals. Eating healthy can be a good habit as much as eating unhealthy foods can be a bad habit. 

Leave some room for failure with habits, as we should leave room for failure in most aspects of our lives because failure is part of Being Human and somewhere along the line you will fail and it's ok, so if you are trying to quit smoking and you had a cigarette when you weren't supposed to it's okay to a certain extent.
When you do make mistakes or you have one or two failures it's important to take ownership.

Common mistakes people make with habits

1. They don't give themselves enough time,  they rush it,  in other words, they are impatient.
2. People don't take it easy on themselves,  so once again being very self-critical on a daily basis.  for example today I didn't achieve my goal so now I am angry at myself and feel like a failure because I didn't achieve today's goal. NO! Take it easy.
3. People are not consistent.  They want to adopt a daily habit but they are only willing to practice once a month or once a week.  that, of course, will not help you in building that habit if you are that inconsistent. 

Building new habits or breaking old ones can really be complementary to each other.  you would find it easier to break an old habit that you are currently struggling with while you are adopting a brand new one.  The new one is drawing attention away from the older bad one,  and if you do eventually get into the position where you are performing the bad habits, the new good habit will be motivation to draw you away from the bad habit if that makes any sense.  

So some scientists call it replacement behaviour: you replaced the bad one for the good one.

There's no real time frame when it comes to breaking a bad habit,  it's unpredictable but yet again we would work on the rule of the average person and according to science. So let's just say roughly between a month and 2 months for argument's sake.

Just planning, for now, is okay. Remember to add actions to your planning and continue to improve yourself and add one or two more good habits whether they are social, unconscious or activity-based.