Unfortunately - much like Grandfather himself - there isn't much nuance.
Avoid getting bogged down in combat, you want ranged damage on these guys as far as possible.
Pick a unit and focus everything on it - even a single Nurgle model can be an annoying speed bump at an inopportune moment.
Look for synergies that boost hit rolls or wound rolls.
Especially as with Daemons battleshock can largely be ignored.
Like I said, no nuance...
Oh, and kill nurglings. All of them. In scenario play these guys will cause you more upset than just about anything else in the grotty armoury.
Other than that, anything that can restore wounds or summon new units is your next target. Easier said than done, so look at some resilient chaff units to bog down the infantry so you can do that.