Experience will be your best teacher,
a starting point of 2 parts water to 1 part glue, (heat to 140° for an hour) then the run/drip off a brush is one test, I add water till the thread just starts to break into drops.
Test the tack between thumb, and forefinger, and watch the strands of glue, learn the feel, time, and the look. Experiment with different consistentcies, with both tests, also put a drop on different types of wood, and observe.
I use different consistency of glue, for differing situations, the temperature can be increased (slightly) to make the glue run thinner without weakening, but this will shorten pot life. Damaged or old glue feels snotty, or rubbery, when tack testing with thumb and forefinger.
On thin pieces, you can balance moisture content by dampening with water to reduce curl, but be careful, too much can weaken the joint, this is true of cleanup as well. It is often better to wait for the glue to gel, and remove it mechanically, than to dissolve with water.