How can I increase my DPS on WoW?

I'm a level 80 hunter and my dps is trash. I can barely get over 2k sometimes, and my group makes fun of it. :( I'm a marksman hunter too.

http://www.wowarmory.com/character-sheet.xml?r=Frostwolf&n=Aeterna
is my armory link. :/
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