There are many tricks for creativity. One that I like to use is to ask yourself questions to which you don't have an answer. From my experience, the best ones are those that require you to write a list, the longer, the better. Most people tend to stop looking at the first answer to their question, so allowing multiple answers is a way to make people look for more solutions.
A trick that tends to work, is to ask for all members of a group that satisfy a condition. Asking for the best members is not very good, because the human mind works like the cache of a computer. It looks first within a small list of elements from the recent memory, and if none of these work, then digs deeper into memory and search for a matching element. So, when asked for the best music band, a person will name the best group from that small list. If the person is required to think more than ten seconds about it, it is almost guaranteed that he or she will find better answers that are deeper in his or her memory.
An example question could be: "What are all the things you can do to a card?". It is interesting to explore not just the desirable actions, but also undesirable ones, to prevent unexpected problems that might arise; you might include some blank cards just in case a card gets lost or damaged. For this example, I'll restrict myself to just positive uses for a single card, ignoring decks and card-to-card interactions.
Good things you can do to a card:
Turn it sideways.
Hide info in the other side of the card.
Flip it.
Throw it to the air or to a hat.
Put it in some place/zone.
Pick it from some place/zone.
Set any number of values on it.
Spin it.
Memorize it.
Depict something in it.
Give it/Pick it from another person.
Cover it, totally or partially.
Put small things over it/under it.
Rate it.
Put opposite elements on different sides of the card.
Assign different meanings to it in different contexts/zones.
Put it horizontally, vertically, or inclined.
Give it a different shape, color or size.
Activate it (the rules should explain how to do it).
Talk to it.
Turn it sideways.
Hide info in the other side of the card.
Flip it.
Throw it to the air or to a hat.
Put it in some place/zone.
Pick it from some place/zone.
Set any number of values on it.
Spin it.
Memorize it.
Depict something in it.
Give it/Pick it from another person.
Cover it, totally or partially.
Put small things over it/under it.
Rate it.
Put opposite elements on different sides of the card.
Assign different meanings to it in different contexts/zones.
Put it horizontally, vertically, or inclined.
Give it a different shape, color or size.
Activate it (the rules should explain how to do it).
Talk to it.
Not all of these are useful, but the more design tools, the less restricted I will be while designing my game. For this reason, I'll add more ideas to this post as they come to me. I'm going to reserve card-to-card considerations and alike for another posts if there is enough interest, so say what you think about it!
