In addition to my current project of converting all existing scenario to version 1.9, I am also creating new normalized scenarios when needed, to make them more suitable for play against the AI. For each scenario, I am doing the following if needed:
1. Add victory conditions
2. Add alliances
3. Limit factory numbers
4. Build cap unique units
5. Anything else which confuses the AI
Victory conditions are important when the playing the AI because it makes it easier to test a scenario for balance before playing. Also games, should come to an end. Normally I will set economic victory at level 2/3 of the map (1/2 in 3 alliance games)
Alliances are an important part of any game. In a complete free for all, only strong nations starting the edge have a chance. Alliances are also more realistic, 3 sided wars are rare and free for alls don't happen, as it would be worthwhile for weaker nations to ally. Some scenarios have no fixed alliances but have political rules, those scenarios don't need to be fixed.
Factories are present in every area in some scenarios. I don't like this, factories form an intermediate objective in TripleA, making for a more interesting scenario.
Unique units should not be allowed to be built in unlimited quantities. Factories producing Wizards, Nazgul, Dragons and the like violate the logic of the situation. Even some WW2 scenarios have some unique units, which should be treated as such.
The AI can be messed up by some other situations, such as games with little or no production on the map.