Matt at Three Plus Plus has done an amazing job breaking down some fundamental and advanced tactics with cover saves. 

An excerpt of some of his tips below. If you found that helpful you should really read the entire article here. Great job Matt.

And here’s one to bring a tear to the eye of general’s commanding less shooty-armies.

Killer Tip 4: Use Focus Fire to shoot your pistols at low cover save models at the back of enemy unitsbefore you charge. You can kill enemies without shooting yourself out of range and causing your assaults to fail!