The answer to the question is: you do it as much as possible without any reference to the other side’s deck.
For example:
If you see a creature and are unsure whether it’s going to be a threat or a blocker, you look at the top of the opponent’s deck to spot what you can steal. Similarly, if you see a creature you can use to block an opponent’s creature, or a card you can play on an opponent’s upkeep to force them to remove an enchantment that they may have, and it’s something you want to play on your turn, you play it and use it immediately while you have access to a removal spell you might have. The same goes for spells that will do the same thing on your side of the board, such as the ability of Nissa’s Renewal to exile a creature or turn it sideways if you need to.
If a creature is unblockable or untargetable because you’re planning to play it with a specific effect (like the +4/+4 ability of Gideon, Ally of Zendikar) you won’t read it as a threat. You’ll read it as an enchantment that your opponent will have to remove.
A good example of this in a real game of Magic involves the most recent Mirrodin block with the mechanic of “graveyard hate.” This was a powerful effect where you could sacrifice a creature in order to remove a permanent which would then lose toughness until you could get another one.
In the game of Magic you have a bunch of permanents like this. In each game of Magic you have a graveyard and a board of things you’d like to remove. Here are the cards you see in your graveyard:
Now, let’s assume you’re in your opponent’s graveyard and you see this card in a graveyard:
When you look at a graveyard you don’t want to say to your opponent “look at this permanent, and then try to move it somewhere else.” Instead, you want to say “look at this one thing in this graveyard, and then try to move it somewhere else. Now put some cards from this graveyard in some other graveyard, this is bad” or “this is bad.”
A lot of fun.
On a similar note, let’s look at this situation:
You have multiple permanents in your graveyard, and you have a big creature with lifelink with an ability that says “Whenever a creature you control dies, it deals double
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