I know a lot of people are asking about leveling guides and the fastest way to level in SWTOR but unlike older games SWTOR doesn't need a leveling guide. The Missions tells you where to go. If you compare it to World of Warcraft, in WoW you needed a specific third party mod to find quest objectives on a map. It took Blizzard four years to add these convenient tools into their actual game. It was the lack of these tools that made leveling guides necessary. With SWTOR, you are about to learn the easiest, fastest, and fun way to level ...
Do it with a friend!
For the last two days I have been leveling with a good friend of mine, Rammy (ingame name). Now although he's a dude in a dress, his avatar has saved my ass more than once. I would say that comparing it to my last leveling experience in SWTOR Beta where I was playing alone, leveling grouped with a friend has been three times faster and even more fun.
There is no disadvantage of doing Missions in a group. You both get full experience. You both get to bring your Companions, and you end up killing stuff really fast, completing bonus Missions where you need to kill thirty of this mob and thirty of that mob, are done in minutes.
Not only that, but you also get social points for grouping with a friend. These social points unlock unique outfits like the slave girl outfit that Princess Leia wears in Return of the Jedi, or the beautiful white dress that you can see the healer Rammy wearing int he background of this screenshot. These social outfits are orange items, so they can be modified and utilized all the way up to end game.
So get a friend and go kill some stuff!