Star Wars: The Old Republic is still quite a new game.  Which means it’s still a pain in the ass to find resources for builds and such.  Granted, the Jedi Sentinel is a pure DPS class so you can’t go wrong with any tree.  But this spec is a good place to start, especially if this is your first time through the game and you’re just looking to survive until you figure out what precisely the Hell you’re doing.

Jedi Sentinel Leveling Spec

Defensive Forms (1/2), (2/2)
Dual Wield Mastery (1/3), (2/3), (3/3)
Focused Leap (1/2), (2/2)
Steadfast (1/3), (2/3), (3/3)
Ataru Form (1/1)
Ataru Mastery (1/2), (2/2)
Opportune Attack (1/2), (2/2)
Righteous Zeal (1/2), (2/2)
Combat Trance (1/1)
Immaculate Force (1/2), (2/2)
Precision Slash (1/1)
Swift Blades (1/2), (2/2)
Temperance (1/2), (2/2)
Saber Storm (1/3), (2/3), (3/3)
Debilitation (1/2), (2/2)
Blade Rush (1/1)
Insight (1/3), (2/3),(3/3)
Master Focus (1/2), (2/2)
Swift Slash (1/2), (2/2)
Focused Slash (1/3), (2/3), (3/3)

Form

Use the Shii-Cho Form until you receive Ataru Form.

Companion

Go with the T7 (Range Tank) right to 50.

Rotation

Force Leap > Blade Storm > Zealous Strike > Force Sweep > Master Strike > Slash > Strike

At Level 30: Force Leap > Blade Storm > Zealous Strike > Precision Slash > Master Strike > Slash > Strike

At Level 40: Force Leap > Blade Storm > Zealous Strike > Blade Surge > Precision Slash > Master Strike > Strike

So there you have it.  Now go ye forth and kill, kill, kill.