If your pool was nice and clean at the time of shut down, and you kept it covered over the winter, your job should be easy. My best advice has to do with the timing. Open your pool while the water is still very cool; sixty degrees or less. And most important, don't remove the cover until you get some sanitizer in the water. It may look pretty good when you peak under the cover but there are probably a lot of microscopic algae plants just waiting for 'ole sol to green them up. Leave the cover on. Fill your pool to the proper level, set your filter valve to "recirculate" or "bypass" and turn on your pump. Ensure that your skimmers are free and clear and that you are getting good circulation. If you have one, turn on your salt system control to 100% or hit the Super-Chlor button. After five or six hours, check your pH and balance as necessary. If you do not have a salt system, now is the time to add some chlorine. For this purpose, I like the granular Di-Chlor. It is a little pricey but it will not drive you crazy trying to fix the pH. It also contains Cy-acid, the stabilizer that will protect your chlorine from the sun when you do remove the cover. If you can feel slime on the side of your pool, I also recommend some high-quality algaecide, but only after the Di-Chlor has been in the water for 8-12 hours.