>Are any items, such as candles, herbs, and the like required to summon?
>Does summoning have to be done in a circle?
>>If so, what is the circle made of?
>>>Is it a few items placed loosely into a circle shape?
>>>Is it a diagram drawn with chalk/blood/magic powder/etc?
>>>Is it people standing in a circle?
>>>>Any people, or do the people require special abilities to be used in a summoning circle?
>Is a sacrifice necessary?
>>>As a gift to the thing being summoned?
>>>>Is this still needed for summoning inanimate objects?
>>>>Do all animate summons require a sacrifice?
>>What sacrifice must be made?
>>>Is the sacrifice the same for every summon, or is it in proportion to the thing being summoned?
>Are any spell books necessary to summon things?

>If circles are used to summon things, how many times can a single circle be used?
>How large of an object/creature be summoned?
>>Can any size be summoned if the summoner is talented enough?
>>Does the size of the summon depend on the size of the circle?
>>What happens if a summoner tries to summon something that is too big? (Either due to the summoner’s strength or the size of the circle.)
>What happens if someone tries to summon something without the proper items or sacrifices?
>Is there a limit on how massive a summon can be? (“Massive” takes things like density into account; you could have a huge wraith-like monster have the same mass as an apple in your setting.)
>>Does there have to be a certain size:mass ratio for a summon to work?
>Can both creatures and objects be summoned?
>>If creatures are summoned, can they choose to ignore the summons?
>>>If they ignore the summons, how long will it take the summoner to know this?

Other considerations
>Can anyone learn how to summon or are certain people born with the ability?
>Is summoning a type of magic in your setting?
>>If so, is it the only type?
>How much time does it take to summon something?
>>Is this dependent on size of the thing being summoned?
>>Is this dependent on strength of the summoner?
>Is summoning seen as a last-resort method, or is it commonplace?
>Is it possible that a powerful enough summoner would be able to forego rituals and circle and just straight-up summon something?
>Do intelligent creatures even give out beacons to people that will summon the creature when the beacon is activated?

A special thanks to @wayside88 for the assist