A typical exercise for game design students is to have them write a "High Concept" document for a game.
It's first necessary to make the students understand that this way of approaching game design is absolutely unnatural. Non-electronic game designers do not write formal High Concept documents, which are marketing documents, before they make the game. They may write something like it when it's time to approach publishers, but at that point they have a finished or nearly-finished game.
The reason the document is created, then, is that producing the programming, art, and other assets for a big electronic game is very time-consuming and costs a lot of money. With few exceptions, the development studios do not have that kind of money (any more than movie directors and producers have that kind of money). So they cannot practically produce the game "on speculation", the way a non-electronic game can be inexpensively produced. Hence they have to describe the game to help persuade someone to give them a lot of money to produce it. The game that comes out of this will be almost certainly be significantly different than the game that was described to begin with, if the job is done well.
The "natural" way to design a game used to be pursued in the electronic game industry, and may still be done for small games. A playable prototype is produced as soon as possible. It is played, revised, played, revised, played revised, seemingly forever, until a stable "good game" has been produced. Perhaps the most famous of all electronic game designers, Sid Meier, did this with Civilization. He programmed, he and (mostly) Bruce Shelley played, they decided what needed to be changed, Sid programmed, they played, and so on. In non-electronic games, you don't really have a game until you have a prototype to play, and then "playtesting is sovereign".
Students often are not entirely clear in their ideas until they write them down. When (back in 2004) I had a much smaller class to deal with, I talked with each student about their ideas before they wrote the document, and found that their "brilliant idea" was only half formed. I'd ask fairly elementary questions about their game and they would have no answer, because they'd never thought about it.
I did not have the opportunity to do that with a class of 47 students (SGD111), but I am sending comments back to each one so that they can revise the document and submit it again for grading.
The concepts tend to be highly derivative of other games, not only because the entire "big electronic game" industry is highly derivative in its offering, but because the students have played games virtually their entire lives, know games that they like (or love), and think of ways that they can improve those games. These are the ideas they are going to present first, of course.
Then the difficulty is showing that their version is going to be better than those well-known games they like.
The High Concept is not about mechanics, but in many cases it is the mechanics of a game that the student says will sell it--better battle methods, for example. In some cases they describe the method, but in some they don't.
Another common theme is "our story is better, deeper, etc." I told one student that unless he had a well-known game writer or novelist on his staff, there was no reason to think his game's story would be better than any other. So this isn't a selling point, unless you can back it up.
Another common theme is "better graphics than" such-and-such. I have to tell the students that almost every "A-list" game strives for great graphics, but few succeed. What will make the publishers think your game will for some reason have truly great graphics? Only a track record for your studio of great graphics, unfortunately. So it isn't a selling point.
Sometimes students will say in their document, "I think this will be a really solid game, so it should be produced". I have to tell them that their belief means little to the marketers and publishers. Yes, they want to know that you believe the game will be really good, rather than something just to put food on your table, but they should be able to tell that from your demeanor and discussion when you talk with them--having it in writing is nothing.
Students sometimes don't understand how important it is to express themselves clearly and confidently. Also, students need to have impressed upon them at some point that grammatical problems may be the "kiss of death" for concept papers. If I'm a publisher, do I want to risk my money with someone who can't even get the spelling and grammar in a short paper right? Maybe not.
In general, designing non-electronic games is actually a better exercise, and much more practical, but I'll have to talk about that another time.
"The worst form of inequality is to try to make unequal things equal." -- Aristotle
"Always do right--this will gratify some and astonish the rest."Mark Twain
"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away." Antoine de Saint-Exup'ery
"Not everything that can be counted counts, and not everything that counts can be counted." Albert Einstein
"Make everything as simple as possible, but not simpler." Albert Einstein