The most important difference between an intermediate and a professional spades player is the ability to count cards. Both players know how to bid and how to play but the knowledge of the pro to know which exact cards are still in the game and who is holding them is the final touch a spades player needs.
Begin Counting Cards
Of course one cannot just start counting all the cards and remember them. This needs practice. As a start one should remember the highest card in each suit. If the Ace and King have been played in a given suit so the Queen stays the highest card left.
Once you remember this you can start focusing on remembering which player already is out of a given suit. Try not to lead that suit anymore since you are giving this player the option to take or leave the trick.
The more and the more you think about which cards have already been played the more you will get trained at counting the cards. You can also say out loud the cards that have been played if you are playing online. Like this it is easier to remember the played cards.
Tip of the day:
In a spades game always keep in mind the current score. Your goal with every bid is to maximize your potential reward while minimizing your potential risk.