King safety is paramount, so don't leave weak squares next to your king. This applies in particular to KB2. Diagonal weaknesses are prey to dropped pieces. Contact checks and knight checks are best because your opponent cannot drop a piece to interpose. This makes the knight a very powerful piece, often worth more than a rook.
Pawns are quite useful for dropping in, to attack and to defend.
It is illegal, however, to drop pawns directly on the first or the last rank. Always keep some pieces held in reserve, rather than dropping them in for no reason. A knight in the hand is worth two on the board. Be on the lookout for sacrifices to create weakness. The game ending combination often starts with a blitz of sacrifice drops to lure the king out of hiding, and ends with a mating net.