A common mistake I see in the spring is mowing your grass too short, in hopes of cleaning out all the dormant grass left over from the winter. You want to mow it shorter than you would in the summer, but not so short that you start to cut down into the crowns in the thatch layer. De-thatching and scalping your grass are not the same thing. Cutting your grass too short can stunt the growth, and depending on the time of year, could take several weeks to recover. Some spots don't recover and become weak spots, where new weeds can easily take root. If there is an excessive amount of dormant grass it's best to run a rake though the grass to remove it, or schedule a de-thatching mow from me. A heathy thatch layer is good for your grass. Don't tell my neighbor down the street I used a picture of his yard as an example of what not to do.
