Honestly i only use skirmishers to redirect and poison stuff.
I know many swera by the cohorts but the unclarity of their rules is too much of a bother for me.
I do love my skirmishers tho, lately thei've started taking a larger and larger percentage of my army points to the point of my army looking like
MSU with some blocks mixed in
EDIT: Ok strategies. Take many small units use them to outdeploy the enemy, redirect dangerous units (especially deathstars) and have the rest of your army fight the rest of his.
Try and get in range of warmachines or just flank low armor units and pepper, overtime the damage adds up and can be quite effective.