Claws are one of the most, if not the most, variable section of the robot with each year. There are some general designs that work year after year, but generally you want to have a unique claw each year for maximum effectiveness. When building a claw, you need to take into consideration every aspect of the objects you intend to manipulate, and possibly have multiple claws for different objects.
Some questions to consider:
How big is the object? In some cases, smaller objects are easier to grab, while bigger ones are harder and require more specialized claws.
Is the object round? Square? Some other weird shape? Use the shape of the object to determine how to grab it.
Are there any holes or indentations in it? Often, holes are the best place to grab an object. Sometimes, you can even design a claw to skewer multiple objects at once.
How many objects can you manipulate at once? You want to move as many objects at once as physically possible or allowed by the rules.
How many can you score at once? This is based off of how large the scoring zones are, and how many objects you can dump into the zones at once.
Some general designs for claws that are useful for inspiration:
A basic claw that uses a pincer motion to grab objects. Very common, and pretty simple, too. VEX sells a premade claw which is (usually) fairly decent. However, this design can only ever grab one object at a time.
A thin metal plate, with rollers above it to scoop the objects up. Not common except in very specific challenges. These are very good at grabbing large quantities of small objects.
Tread with rubber flippers is very good at grabbing objects, and is usually the best way to grab multiple large objects at once.