There are a few basics you can do before signing up with a class.
First and foremost, you never-ever get into a pool without a second person around.
You need to feel comforatable in the water. Most people are afraid of two things; getting their face/head wet and opening their eyes under the water. Throw some pennies into the shallow end of a pool and then pick them up.
Still in the shallow end, start torpedo-ing yourself under the water by pushing off the walls. See how long you can glide under the water. Make it a contest with your buddy, how far you can go and how long you can hold your breath.
We are still in the shallow end of the water here... you need to learn how to relax and float on your back. You should have your arms extended outward and just let your legs relax. If you feel like your sinking or if you feel you've lost your sense of balance, just stand up. It's okay, because this is tough for a lot of people to do. When you're comfortable, try it again. You can use your buddy to spot you too, like weight lifting, have them right next to you ready to put a hand out for if you loose your sense of balance.
When you feel comforatable in the shallow end, go sign up with a YMCA class. It's your best dollar value and instructors all have to take the same class/exam no matter where they teach.
Remember, you NEVER swim alone and don't fool yourself into using/trusting floatation devices.
One last thing I would recommend: Once you learn to swim, take CPR and First Aide.
Best of Luck!