larryd:
Have found that a wiped layer of liquid solder flux gives good results when using stencils and T3 paste.
I don't, because that also gets into the vias.
I do however sometimes add a bit (half a drop) of extra flux from a flux pen to a tub of (used) solder paste.
Workshop temp also has a big influence on the result. I add some IPA when it's a cold.
I look for the pasting/stencilling results. There should be nice well-defined raised blocks on the pads.
Not thin, not smudged. Sometimes impossible to get it 100% right.
Leo..