The issue with Grave Guard is that they're still too fragile and cumbersome to be an optimally effective combat unit. It's simply too easy for the highly mobile armies that dominate the game these days to out-maneuver, chaff, and avoid them.
HOWEVER, GG/TG are still great as a denial unit. You can tie up a really large amount of points into that unit, and with the right buffs there's very little that your opponent is willing to throw at that unit before substantially whittling it down.
That makes it really effective in a gunline army. Two massive units of zombies/skeletons anchoring the flanks, a huge Tomb Guard horde in the middle, all forming a big wall in front of your battery of light/death mages, catapults, and caskets.
The goal would be to make that unit so scary that people wouldn't be willing to go into it without knocking it down a few pegs, with the ranged support to punish them for spending the time doing so.
I'd probably run a blender lord, level 4 to vampires for bubble heals, a tomb prince with GW and magic resistance, all in a big Tomb Guard brick with halberds and razor standard (because they strike at I). Behind I'd have a unit of 20 or so archers bunkering a level 4 LHP on light with mighty scroll, and two level 1s on light with dispel scroll and forbidden rod. Then I'd also have a pair of catapults (unupgraded), a casket, and a hierotitan (or two caskets).
Supporting I'm thinking vargheists for warmachine hunting, two huge bricks of zombies, and a corpse cart (since you won't be moving anywhere anyways). And chaff, of course.
The one thing I'll say about this army, though, is that it's boring as shit. You basically just hole up in a corner and melt stuff with the council. Say goodbye to sportsmanship votes.