A captain I once worked for used to lean over my shoulder to eyeball the compass every five minutes or so. If I was more than two degrees off course, he'd shout at me like a drill sergeant. I know what you're thinking: It's virtually impossible to hold a steady course within two degrees. Well, you're right. And the boat we worked on was a 56' single-screw inboard slug that reacted to commands from the helm about the same as President Bush reacts to commands from the Democratic-led Congress.
However, the experience forced me to focus on the compass and the horizon at the same time in a way that recreational boating never had. And after managing to put up with Capt. Bligh for a year, I also have to (grudgingly) admit that he taught me a hell of a lot about running boats. What's the quickest route from Point A to Point B? A straight line. So let's do it.
Run by the numbers.
A modern GPS is, of course, your first and best tool. But those popular "highway" and "mapping" modes merely point you in the right direction. Can a ½"-long boat icon and pointer on a screen accurately represent your vessel, when the 10, 15, or 20 miles to your waypoint are shrunk down to 8"? Of course not. Instead of guessing with these simple icons, use your numeric navigation page. Most units will show COG (the course you're on, also called "track" on many units) and your BRG (bearing, the course you should be on to get to your waypoint), one directly over or next to the other. Match these numbers to get a straight course. If the numbers differ, correct your course. Realistically, most recreational boaters should be happy with a course that never varies by more than five degrees off the bearing. After a trip or two, you'll quickly become used to using numerics, and notice straighter course lines.
Don't forget about set and drift.
Winds, seas, and currents are constantly shoving your boat off course, and steering in a straight line will rarely result in your boat traveling in a straight line. So as you watch COG and BRG, also keep an eye on XTE or XTK-cross-track error-and remember to steer in the opposite direction to make up for it.