Attitude is a way of signalling when a discard is not involved. The normal rule is to play high if you like partner’s lead and want it led again and low if you want a different suit. This can be played in the opposite way and is called reverse attitude.
If a new suit is requested it can be deduced by considering dummy and the bidding.
A low lead asks for the suit to be returned, usually to an honour. Leading a high spot card (10/9/8/7) shows no liking for the suit and it should not be returned.
If you have a doubleton then play the higher card first. After two rounds your partner will know you are void.
The lead of an honour less than an Ace promises a sequence.
When receiving a lead play the lower of touching honours so not to deny the higher honour.
Having received the signal it is important to refer to dummy to determine the most effective course of action. A strong holding in dummy might indicate that it is not partners choice however a long suit in dummy might show a ruffing opportunity.
When you are ruffing a suit it is important that you know how to get back to partner’s hand for another card of that suit to be led. The size of the card to be trumped signals the rank of the suit to be returned. By taking account of dummy and the lead the chances of finding the right return are greatly improved.
Remember that the declarer can read your signals. If you don’t want to give away your hand, than don’t signal.