1. get as many cheap shots in as possible, get as many normal shots in as possible, it really doesn't matter how strong these hits are sense they have low toughness (except nurgle but thats what a HBVG is for)
2. lore of light is godly with the lore attribute giving all magic missiles and extra d6 hits. and the the buffs are great too
3. hordes
4. engineers on your HBVGs, if they like slanesh.... well you should have enough time to get a round of shots off, and why you bring more then one.
im partial to hordes of halberdiers with detachments of free company, they're all going to die in droves, but good news! state troops are cheap and expendable!
lastly, if its a choice of several lvl 1-2 vs a solid lvl 4 wizard, take the lvl 4. you want a chance to shut down a teezch magic phase