For VOG, there are already some good guides in other places on the net, such as
http://www.playstationtrophies.org/forum/destiny/247017-dest.... What I can provide are some tips that worked for us.
- All raiders being in level 29-30 is almost mandatory. All enemies in VoG are level 30, so that means at level 29 you are dealing about 20% reduced damage, and at level 28 you will be doing about 40% reduced. While it isn't impossible you'll be saving yourself a lot of headaches if everyone isn't getting one-shotted by hobs.
- Biggest difference between normal and hard raid is that you cannot respawn in hard except after each checkpoint - you can all respawn at the checkpoint when you wipe though. In other words, when someone dies during the fights, unless they are self-rez warlocks then you might as well not waste time, grab all your ammo and then wipe and start over at the fight. What you should be taking away from this is
DON'T DIE.
- Look for other people in destinylfg.com, destinylfg.net, and /r/fireteams as they are currently the best place to find groups, some of which have done VoG many times. They can be good sherpas.
- Note that even if you have a decent group with good communication who know all their respective roles etc. it doesn't equate to success. Mistakes and dumb RNG can happen but practice makes perfect - took me three days in joining several groups did I finally manage to find a group that can successfully kill Atheon.
- With the new patch at the Atheon fight the teleports are random, so everybody should know how to use the relic. Might be a good idea to get some practice with it in normal.
- If you only care about the achievement and not the loot in between then you can probably find a group who has an Atheon checkpoint. All you need is to kill him (which can be difficult in itself) to earn the achievement and have a chance to get the best gun in the game, Vex Mythoclast. Also, raid helmets are rewarded only on hard mode Atheon kill.
EDIT (10/07/2014): Interesting video (not mine) I found that you can sort of "cheese" Atheon. Haven't tried it myself but supposedly works on hard.
EDIT (10/29/2014): Patched.