My first tip is to play spells after combat. This way your opponent doesn't know what is coming. The only spells you should play before your attack are spells that will help your attack. Spells like Bad Moon or Raging Goblin could help your attack.

Another tip is to wait to play your instants. For example, lets say you draw a terror and want to kill your opponents Grizzly Bears. Wait until your opponent attacks you with them. They might play a creature enchantment on it, and then you would be destroying two of there cards for only one of yours! You can also play instants at the end of your opponents turn, so you can use your mana for other things if you need to.

Bluffing can work well in Magic. For example, say you attack with a 2/2 and your opponent has a 3/3. If you have an untaped forest, your opponent might think you have a Giant Growth in your hand, and not block, even though you don't have a Giant Growth in your hand. Don't bluff to much, though, or your opponent will start assuming your bluffing.

My last tip is to hold extra land cards in your hand. This is useful for two reasons. One reason is that if your opponent plays an Armageddon, or any other spell that destroys all land, you will be able to recover faster. The second reason is your opponent might think you have some usefull spells in your hand when all you have is land