I've always dutifully prepped flowers the same basic way: Bring them home in a bundle, snip each stem under a running faucet using scissors, then plop them in lukewarm water and arrange. But a little digging around recently about how to keep hydrangeas alive for longer mentioned "shaving" the stem ends so water can travel more easily up to the flowers, keeping them perkier for much longer than if you crush the stem with scissors.
While my first experimentation with this method failed, I can chalk that up to the dull scissors I was attempting to use like vegetable peeler (don't do this, please). But I got a proper tutorial at a workshop put on by L'Atelier Rouge, an NYC floral and event design company that was attempting to teach me how to glue glitter to a rose. Call me crazy, but I was much more enchanted by the technique they advised for stem-trimming: Use a sharp pocket knife designed for the purpose, and work at an extreme angle, like so:
The knife I'm using in this video is a simple Swiss Army knife (which might be a knock off, because I can't find it online) with a single blade and no other functions; they let us take it home for free. Holding your flower stem in one hand, point the blade away from you and gently slice it through the stem at an extreme angle, so the cut reveals a generous opening (like you're cutting a scallion on the bias). If you'd like to do so under running water as well, go right ahead, and either way plunk them right into a vessel of lukewarm water as soon as you can.
Don't try to cut the stem like you would a banana, while holding the knife with your fingers and pushing it through the stem towards your exposed thumb, because stems can be thick and resistant and you're likely to cut yourself—I mean it! This happened at the glitter event and there was blood. Instead cut away from yourself (just like your mother taught you).