Well worded rules and no spelling errors make a good game system. :wink: But that's all done after the basic machanics are in place.
Regarding machanics:
1. Keep "special rules" to a minimum. A special rule for each unit brings out the "rock, paper, scissors" effect in a lot of games. Like Warmachine. Unless that's the point of the game of course such as game systems that are squad or individual in size. Note that I don't mean "stats" shouldn't be unique or highly variable. There is a difference.
2. "Pre-game" actions (movement, shooting, etc) SUCK. If it's something that is done during the game, then it should be done during the game.
3. Little to no paper work.
4. If it's a wargame, go for the "feel" not the "gamey" aspect. Meaning if you are putting together a Platoon level game, design it so a player is a platoon commander*. Keep away from the need to "get that right combination at the right moment with special rule X" for the win from being too obvious.
5. Something I like that others sometimes have problems with: Premeasuring. I personally like games where I may premeasure. Games where people with better spatial ability simply perform better does not make for a fun game and frankly I think the "can't premeasure" rule is used to hide crappy game mechanix.
*See the game "
Disposable Heroes and Coffin For Seven Brothers" on how to make a good platoon level WWII game.
"Grande Armee" for how to make a Horse and Musket large battle game.
"Armies of Arcana" for a superior fantasy mass battle game. "A Call To Arms" because it's cool and SST v1 is certainly better than other Sci-Fi games of course.