This guide is meant to show a player the most efficient way to complete all quests available for a particular zone. If you know of a better order or method to accomplish this, your input is welcome (in fact, greatly desired). For major changes, feel free to edit, but make a note in the talk page as to your reasoning.
Travel north along the road until you come to a split. Take the eastern fork. You will eventually come to another branch to the north, guarded by a tower. Following the northern branch a short way will take you into Splintertree Post.
Speak with the flight master to get the flight path here.
Pick up the following quests from the area:
[30] The Lost Pages - you will be collecting pages to complete this quest throughout your time in Ashenvale. These pages also often make their way to the auction house, so check there if you are missing any by the end.
While Splintertree Post is a major questing hub for this area, the early quests will originate from the Zoram Strand. To get to the Zoram'gar Outpost, head out of Splintertree and follow the road west. Stay on this road until you reach the night elf settlement, Astranaar. You will need to bypass Astranaar by either walking around the lake or swimming through it. Return to the road when you can and continue east. Eventually the road will turn north and pass another night elf outpost known as Maestra's Post. A faded path branches west just after the post - follow it to the coast. Zoram'gar Outpost, the Horde outpost in the area, can be found on the southern tip of the coastline.
Pick up the flight path.
Pick up all quests available here except the one from Muglash.
Hunt naga, moving up the coast. When you reach the northern tip of the coast, you should see a stone structure. Enter the structure and dive into the water there. You will surface in a cave underground.
Complete [22] The Essence of Aku'Mai: Along the walls in this area, you will see sapphires. Loot them to complete the quest.
Complete [19] Naga at the Zoram Strand: Return to Zoram'gar, killing any remaining naga needed to complete the quest along the way.
Turn in completed quests, accepting any follow-ups.
Complete [23G2] Vorsha the Lasher:Once you are prepared, speak with Muglash to begin the escort quest. You may want a group for this, though it can be soloed. Be prepared to deal with up to three mobs at once, with the help of the NPC.
Head east until you find the road near Maestra's Post, then turn south. Shortly after the road turns to the east, you will see a faded trail branch off to the north. The trail leads into Thistlefur Village.
When you reach the northernmost part of the village, you will come to a cave known as Thistlefur Hold. Enter the cave and search for chests, which will contain [Troll Charm].
Once you have enough charms, return to the entrance and take the downward sloping branch. You should reach a large cavern with a lake and a caged bear.
When you are ready, speak with the bear (Ruul Snowhoof) to begin an escort quest. This quest can be fairly difficult, so you may want to gather a group before attempting to complete it. If you are planning on trying it solo, clearing out the mobs between Ruul and the cave exit is a good idea (the mobs outside will respawn before you get to them). There will be two ambushes during the escort - one inside the cave and one as you are leaving. In addition, Ruul walks straight towards a camp of furbolgs once outside, with the possibility of several patrols. Try to pull any groups that may intercept you ahead of time.
This is an excellent time to try the instanced dungeon Blackfathom Deeps. You have completed the only prerequisite quest for the dungeon, and should be able to get both [26D] Allegiance to the Old Gods (2) and [27D] Amongst the Ruins from Zoram'gar Outpost if you don't already have them. You will need a full group of level 20-30 characters to be successful in the dungeon. There are a few tricks to this place, so check out the walkthrough for some pointers.