When do I start?
Rake once the weather warms and you see a little growth. You can then add a lawn fertilizer and fill in any holes with a good soil and re-seed. You can also top seed the whole lawn if you think it needs it. After that, keep it moist so the seed germinates. Top seeding helps to keep the weeds down and make for thicker and healthier lawn.
I remember watching an episode of This Old House where they said to throw lawn fertilizer on when it is about the last snow to give your lawn a pre-spring boost. In the Seattle area we kill moss in mid to late March depending on weather, wait 4 weeks, thatch out dead moss and rule of thumb is grass seed down last weekend in April here, to help fill in thin spots. As far as what you can do now, weeding sometimes never ends, trim back any perrenials that have now died back, and we always like to get tree trimming and pruning completed by end of February so the trees and bushes can just go for it whenever they get enough spring weather. I would also be spending rainy stormy days planning out any new plantings and or researching for the best choices.
Not knowing where you are this article is basic