February is the month to put out pre-emergent herbicides to stop the vast majority of weed seeds before they become troublesome this spring.
Stop crabgrass, dallisgrass, annual bluegrass, and other grassy weeds with an application of Hi-Yield Dimension at the rate of a 35# bag per 7,500 square feet; you can additionally head off dandelions, clover, and other broad leaf weeds by applying ferti-lome Gallery, using one 10# bag per 2,000 square feet.
Seriously, this is the best thing you can do to head off loads of work or an unsightly lawn later this season. Grassy weed control is harder after the weeds sprout, but one application of pre-emergent herbicide now, backed up with another application in early May, will turn a tough lawn challenge into a trivial one.
See our February Gardening Tips for what else you can to do in your garden and landscape this month including what can be planted (trees, shrubs, flowers, veggies, etc).