The single most valuable tool that I can recommend is a "todo" list.
This may take the form of a specialised app, gadget or pen and paper, however the most important thing to remember is that new tasks should be added to the bottom of the list and tasks to be started must be taken from the top - ie. don't cherry pick your tasks, as this will leave you with a task list full of time-consuming (and often boring) jobs that will begin to drag you down.
