You can farm the survivor -> strong security -> high security line (which ends up as +3 valour, -3 acumen) by dropping assassins onto your general.

If he gets survivor after the first failed assassination attempt (I think there are three lines that can arise due to failed assassinations), each subsequent one will cause this line to progress. It's a useful way of training up jedis.

The killer instinct line seems to be harder to advance, and most likely to happen when you autoresolve a battle between a small number of your units and a large number of peasants.

Builder, steward and trader can all be triggered by the player (builder by building anything when that general is the governor, steward by building farmland and trader by building mines) and can have a big impact on province income. The only way to get the steward and trader virtues well-developed on normal generals is to destroy and rebuild improvements though, which some people may consider slightly cheesey.

Failed inquisitions will boost piety, but can also trigger the atheist vice (which drops piety significantly), or born again vice (which boosts piety, but drops dread).

The fervent, zeal-boosting line will automatically appear in a general who spends a few years in a province with very high zeal (above 70-80% I think).

Dread can be boosted slightly by killing prisoners, but it's best to wait until a big battle where you've captured over 1000 to get butcher straight away - killing prisoners too often gives a morale penalty.