There are so many ways to acheive the correct mix, and they are all right, if at the end of the day, you have got it right ... :? Brushes vary as to how much liquid they hold and people vary as to how long they leave the brush in the powder etc etc.
To try to help you, I will tell you CND method and you can give it a try ...
I use a Prostyler Brush.
First (this is if you are starting with a dry brush) fully load your brush with liquid and gently flatten out in the bottom of the dappen dish to release all the air that is trapped in the brush.
Draw your brush gently out against the side of the dappen dish (not just the tip of the brush but draw down the entire length of the hair of the brush) to flatten the brush and to release some of the liquid... first one side and then the other.
Holding you brush so that the handle is straight up in the air ... draw a line in your powder with the flags of the brush, about 1/4 of an inch long.
Then watch the bead absorb the powder. It should take about 2 seconds or the time it takes you to say going ..going .. gone! (like your counting to 3)
If the powder has absorbed straight away, before you can finish saying going going gone, then the bead is too wet. If there is still a load of powder on the top of the bead, then it is too dry-
If too wet, take another little scoop and remember for next time to draw your line a little longer.
If too dry, start again and remember for next time to draw your line a little shorter.
A good rule is that if the product is a bit difficult to handle once you start to work it on the nail (either difficult to control or difficult to press out) then you mix ratio is off.
Once you have the method that works for you - do it every time. You'll need to have a method for small , medium and large beads.
Press onto the nail - and take a breath (again like your counting to 3) - before starting to work the bead. In other words, give the polymerization process a chance to get going for a second or two before you start to press out the bead.
Hope this has helped.