I also find it hard to get command stars per se, although retinue members and traits which increase command in specific circumstances (e.g. when facing particular enemies, when defending, when outnumbered) are relatively easy to come by. However in my experience, because these are not actually altering the base command level of the general, they do not allow him to gain the "night fighter" trait, which is a real rarity.

I also find it odd that, while the majority of my generals have zero command, those who have one or two command stars are described as having rubbish command skills (in the tooltip which pops up when leaving the mouse pointer over the command stars on his info panel). This despite the fact that they are of above average ability compared to the bulk of my family members who have none. Either just having one command star should indicate above-average military skill, or generals should be born with an average of about 3, otherwise it doesn't make sense.

Most of the times when my generals gain command stars, it's as a result of repeatedly tracking down rebels and brigands and kicking their heads in with as few men as possible.