Some time ago I wrote about the importance of using standards as a time saver. Since then I had a chance to apply this approach to several projects where I participated as a test expert.
So, below you can find a structure that helps to collect in one place all info you need to know about the state of test in a project. (I usually build a test plan as a single entry point for all the questions related to test by means of Atlassian Confluence, but I guess any other knowledge sharing system will do).
Also, I can guarantee that if you are able (have enough info, that is) to fill all the sections of my version of a test plan, then you do have your test process under control. So it can function as a checklist and and answer to a question where to start.
My version of a test plan consists of eight sections with subsections. Subsections may vary for each particular project, but I recommend sticking with the top-level ones.
IMPORTANT: Don't duplicate info, don't add info just to fill in sections, it is important that test plan is not just a formal piece of paper.