Filter- Thoroughly clean out/back wash your filter. If you have a cartridge filter, make certain that the cartridge is clean. Your filtration system will play a major part in keeping your swimming pool clear. You want as much circulation as possible. If you have a timer, set it to run at least 8-12 hours per day. You can split the run time (if you timer is capable) in to two different times. For example: 6 hours in the morning and 6 hours in the evening. If you don't have a timer, I would recommend purchasing an inexpensive one or you may need to keep the pump and filter running for the duration of your vacation.
Chemicals- Test your swimming pool water several days prior to your departure and make the necessary adjustments (over several days if large amounts of chemicals are needed). When making adjustments, keep in mind how long you'll be away. If you'll only be gone for a few days (3-7 days), you can simply adjust your chemicals and keep them towards the higher end of recommended ranges (chlorine: 4-5 ppm, pH: 7.8, alkalinity: 120 ppm, calcium: 400 ppm). Adjusting the levels towards the higher end of the acceptable range will help keep your swimming pool from turning green if no one will be around to adjust them while you're away. If you plan on being away longer than a week, I would recommend having a neighbor, friend or a pool service maintain the pool while you're away. I recommend having an automatic chlorinator installed on the pool or using a chlorine floater so that chlorine can be dispensed into the pool. While you're away, you can set the chlorinator to dispense a higher level of chlorine than you normally would (approximately 5-7 ppm).