Hi Neroodragnel,
Like Ienny mentioned Wowhead is a really good source of the ideas on how to deal with specific quests. Just put the quest name in the search and next check the comment window - people most often provide a really helpful hints there. You can also check other things there like gear, Non Player Characters or the whole instances and raids.
Other than that, most of the quests have a pretty good description of the objectives. If you would not be sure you can simply zoom out to the planetary view of Azeroth, Outland & Draenor (right click on the map until you see all 3). You should have all the quests visible on the right at this point (if not - click the question mark button in the bottom right corner). Click the quest that you want to investigate and it should show the area where the quests is supposed to be completed.
In some cases when the quest has multiple locations it may not work, yet it works for most of the available quests.
If still not sure about some details, feel free to ask people in game or on a forum like you did here. If the problem is with just one character, maybe you have a specific addon enabled on this character. To make interface totally clean you can reset it completely.