The ideal conditions for Waveskiën are about the same as for surfing (especially Long board). There is virtually no wind and the waves come in sets with a large interval between them to the coastal reels. The minimum height depends on the power that the wave has, but usually you can start from 0.5 meters.
Each beach has its own ideal conditions, even the tide plays a role in the formation of the waves.
Http://www.surfersheaven.com/old/?page_id=1359 is explained in detail.
Here you will find the sites I use most to get an impression of the waves. There are also more and more webcams, on which you can judge the waves live. For your mobile There is the Surfcheckapp that gives good information.
Also the water reports of the state of the Ministry can be useful to consult.