-use the punch-down fold.
-use water based lube if needed.
-insert the cup into the vagina about 2 centimeters or so (not much at all... just a little past its rim), then push on the base of the cup just below where the fold is to force pop it open. once open, make sure it's able to spin around (this "proves" that it's fully open and in position), then push it on up by using gentle pressure and your vag muscles until it's up as far as it'll go (for me, the bottom of the stem (i never trimmed mine) is about a centimeter away from being "exposed")