The number of rules in a trading system will vary inversely with timeframe, e.g., shorter timeframe systems have more rules than longer timeframe systems.

The number of rules to exit a trade will be approximately equal to the number of rules to enter a trade.

Adaptive rules are more successful in the long run than fixed rules, e.g. a one std dev stop is better than a one point stop.

Simple rules outperform (and outlast) complex rules.

'or' rules are more important than 'and' rules.

Broad rules are better than narrow rules.

A discretionary trader and a mechanical trader will build a better rule base faster than either the mechanical or the discretionary trader alone.