“Don’t get it right, get it written” “Write early and write often” “There is no such thing as good writing, only good rewriting” 
So what do you do to get writing done?
Get free of distractions. You need some time to be alone.
Tell somebody (anyone!) what you are trying to do and then do it. While we need time alone free of distractions, most of us produce a better result when we have some interaction with others who face similar tasks and challenges.
Talk about fear of criticism and find someone who will help you explore what you are really trying to say even if you have not quite got there yet.
There are some really good books, for example Paul J. Silvia, How to Write a Lot : A Practical Guide to Productive Academic Writing. Washington, DC: American Psychological Association, 2007.
Remember that there is no life without mess, and there is no writing without effort.
Non-academic factors make a huge difference to the success and failure of research projects. A high level of research activity places strains on relationships as well as testing the ability of the person doing the research. Self-care, and the care of those you care about is part of getting you to a successful outcome.
It is important to relate to those who understand what the research process is about, and to share your learnings with others about the process as you discover means of survival and success.
While solitary work is essential, it is important to be able to talk about what is going on with more people than just your supervisor. Soon you will know more than your supervisor in a number of areas. You need other experts. At the same time you are responsible to your supervisor and will learn from them about the process and from their questions and differences of perspective.
Look for every opportunity to make presentations which relate to what you are doing. The more your work as such is verbalized, the more you will benefit from testing your ideas and from articulating more clearly what they really are.
Get help when you need it.
 Steve Bevans, conversation with John Roxborogh, Hamburg, January 1998. If you are overly creative another bit of advice may also apply: "strangle your brain children!"