For masters with a lot of fine detail, use a disposable brush and paint the surface of the mold with mixed silicone. You have about 30 minutes before the silicone becomes too thick to pour.

When pouring, do so from a height of at least 2 feet in a thin stream. The thinner the better. Start your pour in a blank section, you get a better result is the silicone oozes / seeps over your masters rather than being layered on from above.

From the Smooth-On data sheet:
"Pouring For best results, pour your mixture in a single spot at the lowest point of the containment field. Let the rubber seek its level up and over the model. A uniform flow will help minimize entrapped air. The liquid rubber should level off at least 1/2 (1.3 cm) over the highest point of the model surface."

Good mixing is critical, some people recommend a double cup method. This is where you mix in one cup then pour into a second cup (scrape the first cup clean) and then remix. Stuff near the wall / floor of the cup tend not to mix well (hence the need to pour into a second cup).

Ensure that the mold stays above 20C / 70F and resist the temptation to demold for at least 12 hours.

From the Smooth-On data sheet:
"Curing Allow the mold to cure overnight (at least 16 hours) at room temperature (72F/23C) before demolding.
....
Do not cure rubber where temperature is less than 65F/18C.
"

That last bit is important as the rubber will fail to set below 65F/18C, there have been reports of molds taking a week to set.

ZombieEngineer