Lesson 2: Promotion

One way to develop extra tricks in either no trumps or suit contracts, is through promotion, i.e, turning middle cards into winners by driving out higher cards. 
Dummy    Declarer
♥ 432       ♥ KQJ

The opponents hold the ♥A in this suit, but declarer can make two tricks by leading either the ♥K or ♥Q or ♥J and driving out the defenders' ♥A. This promotes the two remaining high cards into winners.
Here's another example when the honours are in two hands. You would promote two winners in the same way. 
Dummy       Declarer
♦ Q62          ♦KJ5

Consider the Order of Play
In order to promote middle cards into winners, you must lose the lead to the opponents a number of times. Keep sure tricks in other suits to help regain the lead later. New players hate to lose the lead because it feels like failure, but remember, you have to if you’re going to promote your middle cards into winners. To lose is part of your plan. You’re only doing it to make tricks later.

What Card Combinations Do You Need for Promotion?
You need to hold middle-ranking touching cards and be missing the top ones.
eg, (1) ♠KQJ54 or (2) ♠QJ1054 or even (3) ♠J10954. Once you've played the suit, and allowed the opponents to win the (1) ♠A, or ♠AK, or (3) ♠AKQ, your middle cards will be winners.