I see each combat roll breaking down like this:
- Pre-Attack Effect,
- Attack Roll and Attack Effect,
- Damage Roll and Damage (or Additional) Effect.
The pre-attack effect happens automatically; by default it's "you fight your opponent." The other two effects are conditional on their respective rolls, and Step 3 is conditional on Step 2. And that's it: I prefer not involving any additional rolls and very few modifiers. For example, to the attack roll I would add:
- Attacker's HD (for Target 20;)
- Magic weapon bonus;
- Defender's (descending) AC;
- Situational modifier, usually in the +/-2 range, based on whether the attacker is at an advantage or disadvantage considering *all* elements of the situation.
And, again, nothing else. That total is compared to 20 + magic armor bonus. Simple, not much to look up in a table at all. And players are NOT told any numbers in advance, just what the opponent's armor looks like and what the situation looks like. Players should not base tactics on raw numbers, but on the fictional situation.
Now, if I wanted to add a "tackle opponent" maneuver, how would I change that? I'd keep the same attack roll, maybe treating all ACs as "no armor", and when judging who has the advantage, I'd compare the Dex and the Move of both sides. But I wouldn't use any other penalty; I see no point in applying a -5 penalty for this or that "realistic" reason... and, in fact, a tackle under these rules would probably be more likely to succeed than a normal attack. A successful attack means the opponent is knocked down. Since it's meant to be a non-lethal combat maneuver, the opponent only takes 1 point of damage if the damage roll is 5+; otherwise, the attacker and defender just wind up on the ground together. Strength and size comparisons might modify the damage roll by up to +/- 2.
Now compare kicking a bench at an opponent in a barroom brawl. How would that work? Standard attack (probably no magical weapon bonus, though...) Situational modifier based on comparing attacker's Dex to opponent's Dex. Successful attack roll means damage, although actual damage should perhaps be limited to 1 point; but a 5+ on the damage roll means the defender trips over the bench, maybe with quadrupeds (if it's a really weird bar...) having a -1 on the roll. Again, the maneuver isn't that much harder than a regular attack roll, so players are encourage to try anything they want, instead of saying "oh, tripping an opponent would be a -5 modifier, so maybe I shouldn't waste my time trying to trip anyone."
So my process for creating maneuvers is mostly just deciding what the three effects are going to be and whether there's regular damage, limited damage, temporary damage, or no damage. Modifiers are low and not specific to a maneuver, so I don't need to keep a list handy.