Reading Is Fundamental. In a head sea the waves and the water are an open book. After all, you're staring directly at them. Look for green water and avoid white water. Because its full of air bubbles, white water doesn't provide as much buoyancy as green. Propulsion and helm response can be sluggish in aerated water and cavitation is more likely, too.
Don't Break Dance. Breakers leave no room to maneuver, and the troughs behind them are steeper than those of non-cresting waves, which also leaves no maneuvering room. If you find yourself having to deal with a breaker, power up the face and get the bow over the top, then come off the throttle and allow the boat to settle as easily as possible into the trough. You'll probably drop, but that's better than launching and falling. Dropping into the trough might jar you, but it won't be nearly as bad as the fall following a complete launch off the crest.
Keep On Keepin' On. Sure, rough head seas are unpredictable, but you can sometimes anticipate waves in a set. Always choose the path of least resistance. Use the Mountain Pass Theorem, which states that the pass lies along the lowest point of elevation through the mountains-a saddle point. Look for the same thing in waves. Forgive the sailboat jargon, but tacking is often the best bet. Work your way over each wave and vary your speed and angle of approach to account for differences among them. In the conditions we were in, an approach of 10 to 25 degrees was best-instead of straight ahead-then a hard bank to port to keep the hull connected to the water. And each time, we increased speed on the way up the face, then immediately reduced speed to avoid a hard impact. If you find yourself approaching a wave straight ahead, use a slight angle when coming off it to avoid falling off the cliff.
Go into a head sea knowing that you won't get through without pitching and banging...but you will get through it in the end. Oh, and thanks to Kevin for not letting "my friend" relinquish the wheel.