I finished all my quests on my planet but im still not the highest lvl to go to nar Shanda
If your following a typical leveling curve, here's how it looks (i.e. what level you should be at to start said planet):
Dromund Kaas (Corusant for repub) - lvl 10
Balmorra (Taris for repub)- lvl 16 - 17
Nar shadaa - 21-22
Tatooine - 24-25
Alderaan - 28-29
class story chapter 1 finale - 31 - 32
if you reach any of those planets before the level described above, you did not do all the quests available. period. even with power rushing toons through, doing nothing but all the quests i am of the right level, even if its right on the mark (such as hitting Nar shadaa a few points before level 21...done that before and I was fine.). But if you find yourself in that predicament...
1) you probably missed some side quests. there are odd spots with quests on every planet...gotta keep your eyes open.
2) your stealthing past all the mobs instead of killing a few along the way.
3) your letting a higher level group up with you to assist in the quests.
I have leveled over a dozen toons on both sides past alderaan....you simply cannot get through the game doing all the quest and not being high enough unless you fall unto one of the 3 categories i mentioned above.
Here's a quick tip: keep all the Heroics for the planet you are on in your quest log. keep your eyes on chat...with the new server mergers, there's always heroics going on. just be ready to reply...or better yet, start a group yourself.. "LFM for Heroic 2+ shooting stars" you'd be surprised at how fast people will usually reply. a decent heroic on level is worth a 1/4 to a 1/2 level minimum. ill usually keep an eye open for groups forming for the Heroics, and ill be able to grab at least 2, even if im rushing through a planet