Clip bottoms. (Use a lopper—a strong cutter you can find at your local nursery—to trim stems that are thicker than your finger.) Make an X in the base of each with a pruner; splaying the branch bottoms will help them absorb water. Trim off twigs that will fall below the water line. Fill the vase halfway with water, then add a bag of clear marbles (sold at nurseries, about $3); they’ll give the vase weight and hold the branches exactly where you dig them in, so they won’t lean awkwardly against the side. (Stick with an opaque vase, which will hide all the trickery inside.) To improve the final look, you can snip a stray stem or two, but clip only at the joints, so the tips look natural.