This is something a lot of people debate what works and what doesn't Dre, but my method's worked 90% of the time... I do break a torso now and then though, but I know of no perfect technique every time... When you work at scoring the seam, it leaves marks I don't care for so I tend to prefer a break with needlenose pliars.
I'll walk you through what I use, and how I do the technique as best I can... As always too, if you're looking for some good explanations on basic (and more advanced too) techniques, check out www.FFURG.com
because there's tutorials on our site that are just there to help including separating figures.
I bought a cheap chinese made set of detail work pliars at Sears. They're a must-have. They're sturdy, but about half the price of a US made craftsman set. You can't get them replaced like the craftsman ones though, so when you break 'em you buy a new set, but they're cheap enough I suggest having a set even if you have a craftsman set. These are good for your dirty work, so to speak.
The set has like two wire cutters of different head styles, some gripper needle-nose, etc... But the set I use most is the LONG thin needlenose pliars, they're best for torso splits because they give you leverage for yanking torso's apart, but they also are long and tapered, and very thin, so what I often try first is sliding the figure's arm hole down the pliars and watching for any stressing of the plastic... Sometimes it'll break clean as can be just by doing this, sometimes not.
Now, here's the deal...
Step 1: Boil & pop figure completely (this is just what I do, if you don't need the legs popped so be it... I pop everything so I'm workign with a clean slate)
Step 2: Take the torso (now head and armless). Depending on how thin the figure is, I sometimes dremel the post in the center of the torso. The post that helps hold it together. At times this is fused itself and makes a pop hard to accomplish cleanly, other times it's just because I can fit the pliars down in easier INTO the torso because there's no post.
If you wanted, you could do this with every figure but be careful as the friction from the dremel bit can distort the neck hole while you're trying to dremel-cut the post inside... I use a grinding bit to do this btw, it cuts through plastic with less melting.
Step 3: As I noted, I often slide the torso down the pliars (they're closed btw), and slowly watch for stressing at USUALLY the middle-back, or around the arm-holes. As I said as well, sometimes a figure pops apart just by doing this. I popped something the other day (forget now) and this is what happened. Clean as can be pop. Other figures are tougher though... For instance, a female Jedi Stass Allie's torso became problematic for me at one time. Was a real bitch to cleanly get her torso apart due to the thinness of the plastic.
Step 4: So if it doesn't break cleanly and you're just not lucky with above, you can slide the pliars into the neck hole... If you left the post in tact and didn't cut it, I tend to try to have dremeled the post area so the pliars are wedged into the cut between the two post halves. This acts as a brace, and a good center point for popping the figure apart. Case in point, I did this with the Saga Endor Rebel Soldier because he has a thinner torso, and I had to cut the post.
Step 5: Once you get the pliars inside the torso sufficiently (I usually try to get them as far down itno the neckhole as possible for leverage), now it's time to yank the figure apart... What I generally do, since parts will fly, is I try to cover the torso with a rag, and I do this kneeling on the floor... I YANK the pliars apart hard. I even build up to it with 3 breaths (laugh all you want, but timing this so you yank this open quickly and with good force is important).
Yanking the pliars open is the tough part, and this is more or less the moment of truth. If done right I've got a great success rate with very few misses. Breaks happen, but they're rare and usually because I didn't sufficiently weaken the figure by cutting the post or some such when I knew I should have. Live and learn.
Now, I will say that I've gotten where I can just judge if a figure will break by me shoving the pliars into the arm socket forcefully too. This has worked for me at times...
I'd give cracking some torso's like this a go by practicing on cheap figures. Saga Endor Rebels are a tougher nut to crack so after you try maybe a POTF2 POnda Baba, I'd give a Saga Endor Rebel a go... Just practice a little, you'll likely have a use for the parts anyway.
Hope this is of some help to you though.