Right now is the perfect time to plug or aerate your lawn and/or fields, in the northern US.
Heavily used or walked-on lawns need it once a year. Do it now, then spread some fall lawn fertilizer on it, and over-seed where needed. You can rent the aeration or plugging machines for cheap, for a day or two, from any tool rental place, or Home Depot. Plugging is better than aeration, but either one is better than nothing.
When Spring comes, you'll see a big difference. Remember that lawns are not natural. They are grass gardens - or sheep meadows. If you want them green all the time, try astroturf or write a big check for lawn irrigation. My lawns are too large to afford that.