To get the best results, treat your lawn in the late spring or early summer right after the nutsedge nutlets first sprout. This is because it's much easier to kill when it's still young. Very young plants can be hand weeded or you can use a hoe before they have five to six leaves.
The key to control is stopping the plants from becoming established as they can be a real pain to control otherwise. Shade makes it struggle, so ensuring you have a full turf cover can give good results in stopping it from becoming established. If you need to treat chemically you may want to look at using products such as those based on bentazone such as 3-D herbicide rather than halosulfuron (Prosedge). The reason for this is that so much of the latter has been used that resistance issues have now developed. This means that this chemical no longer works.