Here is perhaps the most daunting task of them all. Coming up with a topic and even writing out a thesis can be fairly simple to do, but it is oftentimes difficult to sit down and actually begin writing the essay. So, here are a few pointers that should help alleviate the process.
Outline / Sketch - Have an outline or sketch handy to help guide your thoughts as you write. Outlines are great to keep your thesis and topic sentences structured. Sketches are useful if you are more of a visual learner. These can be done in various ways. For example, you can make a scattered list of some ideas and link the ones that are connected to form a web-like structure. This would also be a good place to arrange your outline cut outs (Refer to How to Structure an Essay).
Freelance - This type of starting process is very similar to brainstorming. After taking a look at your outline and notes, simply start writing. For this style, it does not matter if you repeat words. Simply go with whatever comes to mind and keep going for about 10 minutes. Afterwards, you can look back and see the different ideas you came up with, as well as edit out anything that you feel is unnecessary.
Keep track of time - breaks are your friends! Taking a 20 minute break every few pages or so really helps you focus and keep up your energy.
Set goals - unless it is a shorter paper, you are probably going to need more than a day to complete the paper so make sure to set goals for what you want to accomplish during your writing session.
The most important thing to keep in mind throughout the writing process is to always refer back to your thesis. Make sure that every paragraph is somehow linked to your thesis. If you notice that many of your paragraphs have a different main idea, maybe you need to refer back to your thesis and do some tweaking.