Wet grass doesn't cut very cleanly, so choose a day like today when the wind dries the grass. I've cut my lawn today with excellent results. Try to brush off any worm casts first, though, or you will squash them into large circular patches.

Bring the height of cut up a bit during the winter. The idea is just to take the tips off every so often to prevent the grass from becoming too lanky. By taking the tips off you are encouraging the grass to "tiller", which results in a thicker lawn.