A good way that works for me is dumping on a piece of paper what are you open point at the moment you are left, could not be the best (or only way) to handle it but it's fine .

Eg. Yesterday i've been working on a web form Before to leave: - Check if Button x behave as described by req.1 - Add javascript alert on button y click - Verify that procedure x works for a given impunt

Hope this helps