1. Water deeply and infrequently. Deeply means for about one hour at a time in each zone. I water for 3 hours and my zones overlap by 50%. Infrequently means no more than once a week once the summer heat hits. Water less often until then. This gives the soil surface a chance to dry out completely between waterings. Weed seeds need much more water than this to germinate. The turf will survive because it gets moisture from the soil. Deep watering will give the soil plenty of moisture to go a week.

2. Mow at the highest setting on your mower (if your spouse will let you). This provides a very thick lawn, keeps the soil cooler (less evaporation from cool soil), and shades out weed seedlings that need full sunlight to take root and grow.

3. Fertilize regularly with the fertilizer of your choice. I fertilize with ordinary corn meal (organic program) on the major federal holidays. They are far enough apart and easy to remember. Next date is Memorial Day

I'd like to point out that if you follow David's advice, all of the "steps" become pretty meaningless.

Many of the problems lawns have are caused by cultural practices. As an extreme example, I live in a desert, but the biggest problem faced by most lawns here is too much water.

I've never had crab grass. I have few broadleaf weeds. I use a weed hound for the occasional dandelion and use the mow high/water deeply approach for the rest.

I meant to point out also that lawns coming out of dormancy do not need fertilizer. Early spring time chemical fertilization is the invention of the fertilizer companies so they can continue to make their boat payments until summer. Large scale grass farmers who fertilize will wait until after the "spring flush" to decide how much to fertilize. For many that happens in late April to May. Then they will apply 1/4 of the year's annual nitrogen. They save the rest for two applications in the fall. The spring flush is going to happen regardless of whether you fertilize or not.

Just to sound contradictory for a minute, I often talk about applying my organic fertilizer in February, three weeks prior to our 'last frost' date. Specifically, Washington's Birthday, a federal holiday. Also my application is one of ordinary corn meal. Corn meal has antifungal properties that my lawn usually needs coming out of the winter. For various reasons (all having to do with having a family that uses the lawn) it usually has some winter time fungal problems. By applying the corn meal, by the time the grass flush hits, the fungal problems are gone and the grass comes up evenly. It also comes up a nice dark green, so there is a slight benefit to the use of a fertilizer early. Let's see if I can summarize...you can fertilize early if you would like it to come in dark green, but the fertilizer generally will not make much difference on when it starts. Fertilized grass will grow faster in early spring, but how many times a week do you want to mow???