!!!IMPORTANT!!! USE YOUR HEARTHSTONE COOLDOWN BEFORE PROCEEDING!!!
Ok, so here's your battle plan.
Let's say you're at the Graymane Wall, staring at the wooden lattice gate.
Here's your path. You go to the right. Go up to the wall and move up the hill. Go past the tree and jump onto the little border. Then proceed left along this until you find a rather large crack. Then, you will hit an invisible wall. move UP along the crack to where you are directly on top of the entire wall. Auto unstuck through it. The autounstucking may take 1-2 tries.
Once through, proceed to search for the part of the wall that goes out forward of your position, where it touches a hill rather high up.
Proceed to jump OVER the hill. You will find yourself in a ditch of sorts. Wall jump forward and away from the wall.
Finish and jump out
BAM! You're in Gilneas!
I would post a video, but I'm a newbie... and MMOwned hates newbies...
All I can say is go to youtube, and go to a random video. Then replace everything from "/watch" with "/watch?v=TsDVSjB_Ntc"