I like to fill in the hole part way with soil, add some water and sort of vibrate the plant in the slurry - fills in the holes nicely... then I fill in with more soil, a little more water, shake plant a little, rest of soil, rest of water. If soil is really great stuff, like I have in one bed, I just back fill all the soil, then give the plant a good vibrating shake - nothing violent... just enough to jiggle loose soil all around the roots and it settles the soil nicely. Level the soil off, water, then add a bit more soil if needed. I don't really push on mine. I never stand on them with feet because I try not to step in the beds.
When planting perennials that were in pots, I do push on soil with hands around roots like Michele describes.
