According to wikipedia, habits are routines of behavior that are repeated regularly and tend to occur subconsciously, without one's directly thinking consciously about them.
Normally a habit is established from doing something on a regular basis and repeating the action regularly. People say that you just need to repeat doing something for 21 days and it will automatically become a habit.
For example, let's say you don't like to shower in the morning. You start doing it for a few weeks it becomes a habit. No matter where you are you won't shower in the morning or you will feel uncomfortable to do so.
Another example would be, if you love to talk on your cell phone while you're driving. At first you might feel it is wrong but as you start to pick up your phone and talk every single time you are driving it becomes a habit. Eventually you will do it without giving it a second thought.
Hence a habit is something that you need to be mindful of. It is not just limited to your actions but also to how you think. This is very critical as if you do not form the right thinking habits you will never be successful. You are what you think.
For example, without realizing it you might be someone with the habit of thinking negative things about everything. Sometimes you don't realize it but you are doing it all the time because to you it is the way you see things. Hence you need to change. One way to change a habit or your thinking habit is to create goals that you can change. I would recommend an attitude goal card with a simple goal that you can push yourself. It does not have to be complicated. It could be as simple as stating on the card, "I am a positive person!". Put the card in your wallet and every time you read the card you are creating new habits. Try it out for the next 21 days, I can GUARANTEE YOU that it can change your life!