You usually call in the following situations:

• When you have calculated the pot odds and they are favorable for you;
• When you need other players to accept you as a loose player;
• When you have a strong hand but the game was opened by a tight player in early position;
• When you don’t want the player after you to re-raise;
• When you want to keep a player in the game who is bluffing and you want to keep it that way;
• When you have a chance to improve your combination later (with draw or free card /s);
• When there are only loose players at the table;
• When you think you have the same strong combination as your opponent, so the chances to win and to lose are equal;
• When you have a winning combination and you can raise but you want to keep the other players in the game since if you raise, they can fold;
• When you want to bluff later;
• When you figure that your opponent has a weak hand;
• When you need to convince your opponents that you call quite often, so you can make them stop bluffing