Start writing the first draft
Now that you have your plan and all the necessary research evidence organized, you can start to write your first draft. Make sure you have all the information you'll need nearby so that you won't have to break your flow to go searching for something. Also, if you have perfectionist tendencies, it's a good idea to try to control them while you're drafting your paper as the first draft isn't supposed to be the final draft. In fact, most authors go through numerous drafts before reaching the final draft. Focus on capturing your ideas; you'll catch the errors later in the review stage.
Tip 1: Turn off the spell check function while you're writing your first draft. Those squiggly lines can be terribly distracting and perfecting your sentence structure and grammar shouldn't be your focus at this stage. Just remember to turn spell check back on when it comes time to review the document! For more information on Microsoft Word's spell check function, including how to turn on the advanced style and grammar option, please see Help from MS Word: Grammar and style check.
Tip 2: Always budget more time for writing than you think you'll need. Nothing invites writer's block faster than looming and seemingly impossible deadlines.