You need to be sure that your pool water has adequate circulation, filtration, and chemical treatment so that it remains clean and clear. There are a number of causes of cloudy water. This would include:
In order to maintain adequate circulation, you should run your pool pump at least 12 hours during the summer and 6-8 hours during the winter (pool pumps are designed to run 24 hours. This will most assuredly help prevent cloudy water). Be sure to test your water regularly and add necessary chemicals to ensure proper balance. If your pool needs to be shocked, shock it and run the filter for at least 24 hours to see if that clears it up.
If your pool water still remains cloudy, contact a pool professional to test and clarify your water. Be sure the pool professional checks your equipment to be sure it is working properly. You should also be sure your filter is cleaned at least twice a year.