When it is apparent that one adversary can “ruff” a suit, or when a
“cross-ruff” is imminent, it is important that you guard against such
a contingency by at least two rounds of trumps. Of course, if you
hold the commanding trump, this presents no difficulties; but, when
the winning trump is with the adversary, you should try to tempt him
to hold it up second in hand by refraining from a high card lead. For
instance, with queen and seven of trumps in one hand and king jack
ten nine eight in the other, lead the seven instead of the queen.
If your trumps are in sequence you can often obtain two rounds by
leading the lowest of your sequence rather than the highest card.