Mmmm...carrots! Get your seed in the ground as soon as it can be worked, but make sure you keep soil evenly moist for up to 14 days as seedlings start to emerge. One trick is to mix a little radish seed in while planting the row, as radish pops up in no time both marking the row and breaking through the soil's crust to let those delicate little carrots through later on.
When growing carrots, take a look at your soil type - the heavier, the harder for those roots to push down, and the thicker/stubbier your carrots will be. Rocky ground? More odd-shapes and twisters. Sandy? You're off to the races!