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Keep your king sheltered
Pawns are the king's armor.
Most attacks succeed only because the defender's king got exposed. The pawns in front of a castled king — f2, g2, h2 (or f7, g7, h7) — are its armor. Pushing them or letting them be traded tears open lines straight to the king, so leave them put unless you have a concrete reason.
When you're under fire, the surest defense is subtraction: trade off the opponent's most dangerous attacking pieces. An attack needs attackers — every one you swap off takes the sting out of it and brings you closer to a safe, quiet endgame.
You're defending and your king is castled behind f/g/h pawns. What keeps it safest?
Answer the question to keep going!