What I Learned Designing Games (AGS)

I can't really believe it's been almost 5½ years since I first found AGS. I was an eager, energetic game-designing ambitionist* back then, and I could only wait to hurl out that new Indiana Jones sequel, which I knew was going to be the best game ever, thanks to my design skills.
* Not a real word.

You learn a lot in five years, and it makes you look back and wonder, "Did I really learn anything at all?"
The answer is most likely no.

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Game Design Tips
Making Games is WORK--NOT play: Game-Designing is fun; you get to throw out all sorts of crazy ideas and features you'd ever want to see in a game and wrap it all together. Game-development is hard work; you have to sit at a computer slaving away the hours working on pixels and lines of monotonous code.
The only way that game-development will be fun, is if it is a learning process, and you push yourself to the next level in everything you do. If you already know how to design and develop everything, then it will be a long and tedious process to the finish line.
Plan it out: Know EXACTLY what you want to make. Know who the characters are, how the plot is going to end, why these things are happening, when to implement the puzzles, and where to end it all. It's probably less fun to do this, but it makes your game less of an illogical and crummy mess when it's finished.
Fan-Games are good, but they are superfluous: Everyone wants to make their own sequel/prequel/fan-game about their favorite series. It's fun, because you love that series to death and want to create something in that world, but it's already been done before. RARELY are any fan-games ever good.
Breaking the 4th wall gets old, fast: The best thing about making a game for the first time is including as many in-jokes as you can about other Lucasarts and Sierra adventure games. It makes me feel all happy inside every time I manage to slip another in-joke in about my favorite game. But this is NOT the way to go. Everyone can make an inference to some obscure adventure game, but it is much harder to create an atmosphere in a game, maintain it, and then finish the game and say I created that world from scratch.
Humor games outnumber serious games about 4-1, and a serious game is much harder to attempt.
EXCEPTIONS: If you are going to break the 4th wall, do it in an awesome and good manner, e.g. Secret of Monkey Island, Space Quest, FL-CL.
If you are making a serious game, THEN DO NOT BREAK THE 4TH WALL.
Less Puzzle Games, more ADVENTURE games: It's so easy to create bad puzzles, and it's so hard to realize that they're bad. Adventure games continuously fall into this weird heap of a quest where the protagonist has to collect random items and then give them all to a guy blocking a door and then go on to the next section, where you learn why you're in the next section, where the next guy blocking a door is, and then you repeat. (Unfair)
Start thinking realistically. Start applying puzzles to the situation, and have the puzzles rise out of the situation and the world instead making boring, generic puzzles.
Adventure games DO NOT have to be about endless quests and trading items, reaching for items out of reach, and then unlocking doors. You can do so much more in a game, instead of boring trading tasks. Prioritize your puzzles according to your story, game world, characters, and locations.
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UNIQUE, NEW CONCEPTS: Adventure games are old, and I dare say the standard adventure game interface is flawed (Walk, Hand, Eye, Mouth). The more I use a text-parser, the more I miss using reason and logic instead of clicking on everything.
Adventure games need NEW features in order to survive. Cross the genre and make a hybrid (Quest For Glory), implement new features (New Verb actions like KICK!), totally change the interface (LOOM), or just do something that will make the game different, and a new learning experience to every player. Old adventure games have been designed with the same interface countless times. Pump something new into the genre.
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Besides the above, you can learn specific skills in puzzle-making, animation, backgrounds, characters, story, world-building, etc.