A couple big things, First off, your deck is 70 cards. You must cut it down to 60. You have 18 lands You must run many many more in order to consistently play your cards.
Now for your construction. There's nothing wrong with the graveyard deck concept. There's some strong golgari cards that work with this synergy.
Lands. You probably don't need haunted ferngraf. You do need 4 overgrown tombs and I think evolving wilds could work in this deck as well.
Creatures. There's nothing wrong with arbor elf at the moment. I would consider running Deathrite shaman since you can get value out of your graveyard with it and it can help ramp up. That and arbor elf should help you get some of the bigger creatures out a little easier. Varolz is the card to build around in this kind of deck. His ability is pretty good. Cards with Lotleth troll, Desecration demon and Jarad lich lord synergy well with him. Scavenging ooze coming in m14 will also be very good.
Try the deck below. Some of the cards cost a little bit but I think it has the graveyard theme you want with still being able to play to win. You'd want to scavenge onto something like desecration demon or lotleth troll and just go over they're blockers, and jarad can just fling the pumped up creature at their heads. Deathrite can eat evolving wilds to help ramp up to an early 4 drop or she can eat cards out of your yard for value. Grisely salvage does 2 things. It can get creatures in your yard for varolz/jarad and it can also get something in your hand to pitch for lotleth.
6 Forest
4 Golgari Guildgate
4 Overgrown Tomb
6 Swamp
4 Evolving Wilds
4 Arbor Elf
4 Deathrite Shaman
4 Varolz, the Scar-Striped
4 Lotleth Troll
4 Desecration Demon
4 Rot Farm Skeleton
2 Jarad, golgari Lich Lord
4 Grisely Salvage
3 Putrefy
3 Abrupt Decay
1 (100%)
