Depends on your system setup and if the skimmer is well matched with your current system. There are lots of variables besides the skimmer to know what kind of skimmate you will get. It has to do with the system size (not including the sump), the water depth of the skimmer, the level of the water inside and your water chemistry.
If all the variables are correct, then you should be able to open the valve and lower the water level inside the skimmer. This will cause the foam to dwell inside the neck of the skimmer longer before overflowing into the collection cup. This process will allow for dryer foam to collect at the top before it overflows giving you that very dry skimmate.