If you are playing a more skilled opponent they are likely to see your 1 move threats. As such you need to look for more complicated threats that are harder to avoid.
Tactics in general are moves that gain a clear advantage in material or lead to checkmating the enemy king. Strategy in contrast leads to more long term advantages. Below I discuss three basic tactical motifs.
This is attacking two pieces at once.
Sometimes referred to as a fork when a knight does it.
Below is an example where black forks with the knight checking the White king and attacking the White queen. When white moves his king out of check black gets the queen by force.
Note black draws this game since he can not checkmate with just the knight and king, but it is better than actually losing the game.
Here is another general double attack
Below is another example of a double attack. This double attack is called a discovered check.
Below is an example of the more general "discovered attack"
Gain material in the following games using the concept of double attack and or discovered attack.
A pin is when a piece is unable to move due to a valuable piece being behind it.
A player can take advantage of his opponent's pinned pieces such as in the two examples below.
Sometimes another piece is behind the pinned piece other than a king. Here Black forgets that his knight is pinned and loses his queen as a result.
Happens when a player isn't careful. It's a way of checkmating a castled king.
Note it may be prepared with two rooks often known as a "battering ram".
Players usually avoid it by moving their h pawn up one square. Below is a game in which black does h6 while also gaining time by attacking the knight on g5. The act of moving a pawn in front of the king up one square is known as a luft (means air).
Note that the luft may be under attack as shown below. Note how h7 is guarded by the bishop. Perhaps black should have went g6 instead.
Try to figure this one out.