Growing up and now working in Ohio, I've played my share of rounds in the rain. Some of my most rewarding rounds have come in tough conditions. Golf is an outdoor sport; playing against the weather is every bit a part of the game as water hazards and trees along the fairway. And even more, if you can handle shots when conditions turn tough, you're already one up on the rest of your group.
Be prepared: Not to weigh you down, but do you have rain gloves, extra towels, even an umbrella in your bag? You'd be surprised how many people do not. The goal when playing in the rain is not to think too much about playing in the rain. Those who are not prepared are constantly worried about wet gloves, water dripping down their back, etc. Know that conditions can change -- and be prepared.
Stay controlled: When it's time to focus on the shot, solid contact is more important than ever when conditions get tough. Don't give yourself any easier opportunities for mistakes by overswinging. A common mistake is the feeling that you have to swing harder -- but that's actually the most harmful thing you can do. The chance for the club to slip in your hands or your feet to slip on the swing are only increased in wet conditions. A shorter, more compact swing with more club will only help you in these situations.
Adapt to the course: When it rains, the course changes right in front of you. If you watch pro tournaments when it’s raining, you notice how hard it is for even the world's best players to get their chips and putts to the hole as the conditions get slower and wetter. Be aware of what the rain, cold and wind can do to your shots. Wet conditions mean less spin for shots but slower greens and softer fairways. Adjust your game and club selection accordingly.