If you have a brainstorm list of ideas you're part of the way there. Pick your favorite 2 or three and break down what you liked most about them.

E.g. RTS: liked building the buildings -> make a game centered around only building buildings.

dungeon-crawlingRPG: liked the combat with monsters.
-> make only the combat part. no character choice, no stat or equipment choice, just the killing.

Oh, and don't do it alone, get at least one other person in on it who can keep you sane. If at worst you can't get a developer, at least get someone you can bounce your ideas off of and who can play whatever simple prototype you make and who you can watch try to play it, or talk to while they play it. The second you have anything manipulatable (not balanced, not playable, just does something), get someone other than yourself to start manipulating it. Set yourself a hard core definition of "working" and a hard deadline of "prototyping" hours and pause when you reach them. Set the gamelet down for a bit, like two days, and when you come back to it, re-examine whether you want to continue it or prototype something new.  (I advise that because despite being continually full of ideas, I got myself embroiled in developing a live, legacy game, and 7 years later I'm still trying to get it to a "fun to play" state.)

Luckily, fun doesn't -require- complexity, and often you can add complexity later around a simple core for more options when you find a promising prototype.

If you have a brainstorm list of ideas you're part of the way there. Pick your favorite 2 or three and break down what you liked most about them.

E.g. RTS: liked building the buildings -> make a game centered around only building buildings.

dungeon-crawlingRPG: liked the combat with monsters.
-> make only the combat part. no character choice, no stat or equipment choice, just the killing.

Oh, and don't do it alone, get at least one other person in on it who can keep you sane. If at worst you can't get a developer, at least get someone you can bounce your ideas off of and who can play whatever simple prototype you make and who you can watch try to play it, or talk to while they play it. The second you have anything manipulatable (not balanced, not playable, just does something), get someone other than yourself to start manipulating it.

Set yourself a hard definition of "a working prototype" and a hard deadline of "max prototyping hours" and pause once you reach them. Set the gamelet down for a bit, like two days, and when you come back to it, re-examine whether you can make it fun and want to add another prototyping goal to it or prototype something new. 

(I advise this because despite being continually full of ideas, I got myself embroiled in developing a single live, legacy game, and 7 years later I'm still trying to get it to a "fun to play" state.)

Luckily, fun doesn't -require- complexity, and often you can add complexity later around a simple core for more options when you find a promising base.

If you have a brainstorm list of ideas you're part of the way there. Pick your favorite 2 or three and break down what you liked most about them.

E.g. RTS: liked building the buildings -> make a game centered around only building buildings.

dungeon-crawlingRPG: liked the combat with monsters.
-> make only the combat part. no character choice, no stat or equipment choice, just the killing.

Oh, and don't do it alone, get at least one other person in on it who can keep you sane. If at wost you can't get a developer, at least get someone you can bounce your ideas off of and who can play whatever simple prototype you make and who you can watch try to play it, or talk to while they play it.

Luckily, fun doesn't -require- complexity, and often you can add complexity later around a simple core for more variety when you find a promising core..

If you have a brainstorm list of ideas you're part of the way there. Pick your favorite 2 or three and break down what you liked most about them.

E.g. RTS: liked building the buildings -> make a game centered around only building buildings.

dungeon-crawlingRPG: liked the combat with monsters.
-> make only the combat part. no character choice, no stat or equipment choice, just the killing.

Oh, and don't do it alone, get at least one other person in on it who can keep you sane. If at worst you can't get a developer, at least get someone you can bounce your ideas off of and who can play whatever simple prototype you make and who you can watch try to play it, or talk to while they play it. The second you have anything manipulatable (not balanced, not playable, just does something), get someone other than yourself to start manipulating it. Set yourself a hard core definition of "working" and a hard deadline of "prototyping" hours and pause when you reach them. Set the gamelet down for a bit, like two days, and when you come back to it, re-examine whether you want to continue it or prototype something new. (I advise that because despite being continually full of ideas, I got myself embroiled in developing a live, legacy game, and 7 years later I'm still trying to get it to a "fun to play" state.)

Luckily, fun doesn't -require- complexity, and often you can add complexity later around a simple core for more options when you find a promising prototype.