Spring isn't the only nor always the best time to do prep work. If you need to re-seed patches where the lawn looks bare, just before the snow comes is a good time of the year to start. The seeds will get worked into the soil as the snow falls and lay dormant during the winter months.
Once spring and the first melt arrive then the seeds will be in good mud and the early stages of germination will begin. Once they start getting the sun then good, fresh grass should follown in a couple of weeks.
Crabgrass and its relatives don't thrive in the Fall or Winter and this means that you have a head start on that kind of weed control. As the new lawn grass starts to spread, it has a good chance of stopping the crabgrass, and with any luck it won't develop at all.
Start applying the Spring fertilizer at the earliest possible time. This will help give the young shoots a good start and, if you use fertilizer that also controls weeds, you may solve two problems in one go.
As that snow continues to melt off there will be areas where the grass has become thatched - this is a condition in which the blades get lain over one another, then compressed from the snow pack on top. Some of these may die over the winter and this can leave you with a kind of straw-like covering, hence the name 'thatch'.
Doing something about this is easy. Just cut the grass a little later in Fall than you need to so that the length is controlled. This restricts the height and helps keep thatching to a minimum.
In Spring give the grass a good raking. Of course, if you raked in the Fall, there won't be any leaves to get rid of but the extra raking helps pull up thatched areas and allows air to get to the soil.
If the ground has become hard, or the soil is easily compacted, you can follow that up with an aeration. This can be done either by using a special attachment on a riding lawnmower and running it over the grass, or using special large-drum rollers with spikes poking out.
An inexpensive way is to use special shoes which are like golf shoes with spikes on the bottom. You just put them on then walk around the area you want to aerate. The tiny holes made by the shoes allow air to penetrate the soil more easily. At the same time, it makes channels for solid fertilizer pellets to fall into.
After de-thatching and aerating, your lawn will be ready for you to carry out any weed control and to start seeding, fertilizer application and regular mowing.
