Post by Arideni
The initial thoughts from your post suggest you wish to participate in both 5-man and 10-man content in the future. In order to graduate from regular 5-man content you need to learn and show that you have a working knowledge of the basics.
Your first step is determining your talent specialization. You do not seem too sure what it is you want to do...that is, you do not seem very familiar with your talent trees. Please read over this link -
http://www.wowwiki.com/Warrior_Talents - to help you focus on the different talents of each tree, as you have many options even when going Protection.
Considering you are still 'new' to level 70, you may wish to retain some of your arms or fury talents for the time being so that you can farm gold or complete quests. There are countless quest rewards to help give you decent tanking gear and you should work hard to complete them!
Here is one of the most important articles ever compiled concerning warriors and how to tank properly -
Ciderhelm's Fortifications - Hosted by TheorySpot f.k.a. TankSpot
The most important thing to do first is ensure you have some of the best items for tanking possible so that you may complete dungeons with ease. The most logical thing to do, in my opinion, is to take on a hybrid spec so you may still quest and tank any dungeon that comes up along the way. Read on-
After familiarizing yourself or reviewing the talent trees you may find yourself needing to quest frequently early on. This is a good thing as you earn not only quest items of course, but money as well. If you quested poorly, you have a plethora of items to put together a rag-tag tanking suit. If you picked damage-dealing items from the quests and completed most, then you may need to invest in some starter gear from the auction house. Research items using this website and your local auction house to find the best deals; you may have to get some gear crafted due to the low supply of certain items.
In the end, working towards the quests and dungeon loot to gear up will payoff and you will be able to tell the difference in your ability to tank a dungeon before and after. Once you understand some of the mechanics and denounce mainstream heresy you can be assured you're ready to move on up and you'll know when you're ready, too.