1. Against a no-trump contract, the lead of a doubleton or tripleton, usually when partner has bid the suit, or the opponents have bid the other suits. Sometimes it can be a deceptive play hoping that declarer will think that the wrong hand has the long suit.
2. Against a suit contract, the lead of a singleton or doubleton trying for a ruff is a short-suit lead.
Since South has bid your only long suit, you should make a short suit lead. As East will not hold five spades and fair values (no 1♠ overcall), the ♣7 is a good choice.