My furniture's tee nuts aren't holding. Is there a trick to installing them correctly in wood?

The most common issue is an incorrect pilot hole or inadequate setting. Those prongs need to bite into solid wood around the hole to prevent rotation and pull-out. First, drill a pilot hole just slightly smaller than the tee nut's shaft, *not* including the prongs. Then, use a C-clamp or thread a bolt through the nut from the other side and tighten it down to *pull* the prongs firmly into the wood. Hammering can sometimes work, but pulling provides a more consistent, secure set, especially in harder woods. If the wood is too soft or the hole is too big, they'll strip out, leading to loose connections and needing a re-do.