Important thing: Find where general in unit is and try to engage in way he personaly is not endangered (IIRC he is on left side, so if you must risk being attacked by spearmen, take it from right).
And of course, try to attack enemy general (so attack from his left side).

When fighting, try to zoom in and find yours/enemy general and check whether they are being attacked.

Of course, you want your general be hit few times, so he gain hitpoints trait/ancillaries. But its much better to gain them aginst swords/peasants than aginst pikeman (i wish there were indicator showing general's hitpoints (other than how much damaged he looks like).