This is by no means a comprehensive list, however they are at least some of the things you should think about before deciding whether or not you are in a position to all in a particular target.

-Check your target's level
-Check their experience
-Check their items. How many health/mana potions do they have? Do they have more items than you?
-How many minions are present. Are there more of your minions than your minions? Or the other way around.
-Do they have any summoner spells up?
-Where is the enemy jungler?
-What abilities have they used recently?
-Do any of their items give... Read More