hi Jeff... i am a relative newbie to convex flanges, so i understand the worry of not putting it on correctly...
what i do is.. cut the hole to my stoma size, i then very slightly stretch the hole by running my finger round in it - the ones i've used kind of curl up around the edge of the hole when i do this, and then retract to their original size once in place - then i just apply it as normal, starting from the area under the stoma, and pressing the whole thing into place.
straight away, you need to get the part which encircles your stoma pressed down with a finger tip, all the way round - this will feel like a little circular valley around your stoma. once that's adhered, press the whole flange and hold it pressed with your hand for a few seconds to make sure it's stuck... with many of the convex flanges, you don't actually get the whole area of the flange stuck down, there is a gap of unstuck flange where it rises up... but as long as the bit round the stoma is stuck fast, and also the bit around the very edge of the flange is - that's ok.
i hope that helps, it's really hard to describe in type!!
ps the Hollister ones have just been recommended to me, and i haven't ordered them yet, so let me know what you think of them.