Life: Simply, your life total.
Card advantage: The number of cards on your board and hand, including the number of charges on your weapon. This does not include the weapons and cards generated by Hero ability.
Tempo: This is a more complex term. Simply put, this is the number of minions on your board vs. the number of minions on your opponent’s board. This dictates the “flow” of the game. In HS, most minions cannot attack the turn they are played. Therefore, the player with minions already on board can choose how he wants to trade with the cards you play. Also, he has the possibility of buffing his minions. This gives him a strong advantage and explains why you most likely want to clear his board every turn.
An example of a tempo play is: • Using 2 spells to remove 1 large threat. • Using a mana efficient card (i.e. Backstab) to remove a minion, then having enough mana to play your own minion. Thus, you have more Tempo than your opponent, even though both plays are equal in terms of card advantage.
In HS, you always want to have the right balance between all of these 3 resources. For example, you lose when you hit 0 life, no matter how many more minions on board or cards in hand you have. Also, you can lose if you have more life, but have 0 cards on board/hand vs. your opponent’s 5 cards in hand. Most importantly, you will lose if you keep your cards in hand, while your opponent builds his board. Even if you play conservatively and slowly gain card advantage, your life will quickly drop turn by turn. Then, you will not be able to turn the tides when he has lethal.
As a player, you will have the option to trade 1 resource type with another according to the plays you make. If you hit face instead of trading favorably, you are gaining life while losing card advantage/ tempo. If you wait 1 more turn while holding Flamestrike (so your opponent plays 1 more minion), you are trading life for card advantage. If you are using 2 cards to remove a large minion, you are losing card advantage to gain tempo. The “wrong” play can be as easy as not prioritizing the correct resource. For example, you traded favorably instead of going for face, when you could have won next turn by playing “Fireball” to face.
As a player, you must make the correct decisions in order to choose which resource you want to prioritize. This is the key to winning. The resource that you prioritize may be even directly related to the deck you are playing. Sometimes, life may be more important than card advantage (Refer to Face decks). Sometimes, card advantage is more important than life (Refer to Handlock). Sometimes, tempo is more important than life (Refer to using weapons).
In conclusion, all 3 resources are equally important in theory, but, in-game, you have to prioritize one or two in order to play effectively.
Thanks for reading.