How to Find the Instance Quests
Instance quests are also much easier to complete than solo quests because you don't have to do them alone. This aspect also makes them a lot more fun. Chances are, if you have other level 80 characters and are now leveling a new toon, then you'll discover new quests that you just skipped over before because you had to have a group to complete them.
In most cases, instance quests will be available in the vicinity of the entrance to the instance. For example, when you reach level 60 and move out to Outlands, you should be able to find several quests that need to be completed inside of Hellfire Ramparts. Just start by looking around the towns that are near the entrance to Hellfire Ramparts. However, remember not to stray into towns held by the opposing faction. All instance quests that are available to you will be in a town that's either contested territory or held by your faction.
One problem with just looking for the instance quests on your own is the fact that some of these quests have pre-requisite quests that must be completed before you can do the instance quests. This is where a good instance leveling guide, like Dugi's Dungeon Leveling Guide, comes in. An instance leveling guide is the only kind that was made with instance leveling in mind, and it will steer you toward the pre-requisite quests you need before you can be eligible for the instance quests. Usually these pre-requisite quests are the only ones you really need to do outside of instances, unless you are a DPS and the queue for a dungeon group is excessively long.