Relax. When you see weeds in your lush, green grass, it is easy to get frustrated. In reality though, some weed problems aren't problems. Many plants provide benefit to soil. Large areas of strictly turfgrass, when left alone, become dependent systems with no way to feed or sustain themselves. This changes when you introduce certain plants, even certain "weeds", to the yard. The introduction of these plants/weeds allow the grass to care for itself, apart from mowing. Rule of thumb: if your yard is less than 10% weeds, you don't have a weed problem.

Identify. When identifying weeds, there are a couple things you want to know. Are they grasses (crabgrass, quack grass, etc.) or broadleaf weeds (dandelion, ground ivy, etc.)? This is important because it tells you if they are monocots or dicots. Monocots, or weedy grasses, emerge from their original seed with a single leaf while Dicots, or broadleaf weeds, emerge with 2 leaves. This is important because you want to treat weeds while they are small. You also want to know if they are Annual, Biennial, or Perennial in your climate, because this will affect your method of control. 

Annual weeds germinate, grown, send up flowers and produce seed all in the same growing season. They are ultimately killed by frosts, but you want to make sure you manage them to reduce populations of the plant. If you can, do not allow them to seed; mow or pull the weeds before they get to that stage. 

Biennial weeds have a 2 year life span. In the first year, they store food reserves and in the second year, they flower and seed. Like annuals, you want to do your best to avoid letting them seed. 

Perennial weeds are the more difficult weeds to control. While they germinate from seeds like the other 2, they can also populate from underground rhizomes and aboveground stolons. They cannot simply be dug out due to the rhizomes and do not die off in the winter. The best way to manage these weeds are to change the soil condition that is allowing them to thrive. 

Armed with all this knowledge, you and/or your lawn care service can devise an appropriate strategy to manage any weed problem that comes up. 

Listen. When weeds and other plants pop up in your yard, it is your soil trying to send a message. Weeds needs certain soil conditions to thrive just like your grass, so when they begin to grow you need to reevaluate your soil. Their presence points to a problem with soil pH, soil life, moisture or drought, soil temperature, drainage, organic matter, fertility, tillage, soil structure, and compaction. 

Eradicate. The best way to eradicate weeds is to have a nice, lush turf of grass. When grass is healthy and taken care of, it will block the light necessary for weed seeds to germinate.