I'll talk generalities for now, and add in actual spec trees later when not at work. Not to mention i cant remember ability names worth a damn. This is what i've noticed getting to lvl 50.
You have 2 damage trees as a shadow.
1st is Infiltration (focus on melee) and 2nd is Balance.(focus on force)
What i run with at level 50 is a mix of both.
Personally while leveling i think it's best to go up just 1 tree. The decision on which depends on the play style you like.
Balance is more AOE and force driven. A normal encounter with all cool downs refreshed. Damage boost used and then AoE dropped. This AOE causes your target to take more dmg from your dots. Force breach. Double Strike while stunning/interrupting when needed until you get the proc to instant cast mind crush. Should be done and able to use your finishing move.
Infiltration is go in stealthed, pop black out, shadow strike, shadow strike, stun, shadow strike, shadow strike. Main strike to build back force, double strike, double strike, project. stunning/interrupting as need Project. Main strike, double strike, force breach. In shadow stance you're building up your shadow procs that stack up 5 times that allows your force breach to do serious damage. Double strikes reduce the force costs of your project, and crit force abilities increase your chance to crit with melee.
My level 50 spec is a bit different. While my focus is on pvp i find that it works very well in pve too. Big difference is that i dont worry about any abilities that channel or have cast times. Everything is instant cast. I have serious damage output with instant cast range with force breach, force in balance, project, mind crush(proc). Deadly up close with shadow strike, double strike (reduces projects force costs), and the main attack. I have additional 10 force plus extra regen with blackout. Everytime my force spells crit my melee crit chance goes up. I also have an array of cc with force wave, force stun, mind snap, mind maze (sap), force lift (which will stun for 2 extra seconds when it breaks), slash, force slow, spinning kick.
Plus with being shadow you can also swap over to combat stance and get damage reduction and able to guard/taunt.