Breaking bad mechanical habits

I am so accustomed to complaining all the time that I find myself doing it frequently when I start off the day with the intent to avoid such things. Before you know it; I'm criticizing a rather difficult to deal with boss at work and various other people who are instruments of conflict in my life at this time. How do I stop this complaining? It's a very bad habit and my brain automatically goes into criticize mode on most days. I just automatically find myself doing it. It's crucial that I stop I know. What exactly would be a good first step for a beginner such as myself? I am not yet to the point where I can do in depth contemplation. I have had some moderate success in beginning meditation. I have occasionally seen images. Keeping up practice will improve this. Any suggestions to help me in breaking the complaint habit?