Plan before you write. An outline isn't entirely necessary, but it may help. Still, knowing what you will write about before you write means that you won't have to come up with content on the fly. Don't just have a basic topic in mind. Spend a few minutes before you sit down to write thinking about what you will write and how you will write it. Think about the major points you plan to make and in what order you will make them.
Do warm-up writing. Set a timer for three to five minutes. Then write nonstop for that time period. It doesn't matter what you write about. You can write about what you had for breakfast or things you saw while driving your children to school. The point is that you are getting your brain and your body into the rhythm of writing.
Create an environment conducive to writing. Eliminate distractions, both physical and mental, from your working environment. Spend a couple minutes tidying up your writing area. Turn off the radio or the television. Make sure that the people you live with know that when you are writing you are working and are not to be disturbed.
Create formulas and follow them. If you look at your writing you will probably find that it all falls into two or three broad categories. Create formulas for each of these. Don't look at them as constraints that you can't ever step outside of, but as tools that provide guidelines and structure for your writing.
Group similar writing together. If you have more than one project to complete, do as much writing in one sitting as you can. Your writing speed will increase as you get more into the head space of writing.