So I was working on a Space themed campaign setting, and I decided to have their be a direct analogue to the Jedi and sith in the setting. I was rolling to decide what space faring races in the nearby region of space would function as the local jedi's and I had my picks for a Jedi Master and a Jedi Knight.

When I rolled from my tables on the Knights padawan I came up with a teenage male Drider. Cool, but then I kind of got stuck. How would a drider learn to wield a lightsaber effectively (seeing as their myriad of legs may make it hard to duel with effectively). And even if he does learn to use it well, what of the forms would her specialize in realistically.

As you can see this is a bit of a question for fairly in depth star wars and D&D fans, so I don't expect an answer right away if at all, but any insight at all would be nice, and may the force be with you.

i think having the extra limbs might be an asset in battle, kinda like how pong krell used his extra arms to his advantage by wielding two double bladed sabers. but idk just a thought

Their legs don't have to be a disadvantage. Given that they can lean forwards and still be full balanced, they'll have a longer reach than most humanoids. Climbing up ceilings and walls is always useful, as well, since you can force your opponent to have to fight against gravity to reach you.

I forget whether Maul ever wielded a lightsaber when he had his cybernetic spider legs.  I think no in current canon, because I think only Savage Opres and like a droid actually saw him like that, then the Nightsisters restored him of sorts and rearmed him.  

There was an old EU one shot comic where Maul and Obi Wan fight in Tattooine, Maul has the cyborg spider legs, maybe even a scorpion tail?  I again forget whether he had a saber.  It was a much more drawn out fight than their current canon finale confrontation.

I'm primarily concerned because it would make it hard to do sweeping moves and defensive moves that cover the back without potentially harming ones own legs, in addition to being hard to defend ones entire body from anything other than frontal assaults. They would have a smaller range of torso movement I think and would likely need to focus on a thrusting style with fencing attacks or overhead attacks (which sounds like Shii Cho).

I dunno, don't know how real anatomical this is for arachnids, but I've seen a fair share of spider abdomened/legged and humanoid thoraxes creatures prove quite nimble on their feet, and more importantly hips and knees.  It's got four times as many points to shift its weight.  I could see, say a arachno-Maul, want to sweep along its flank, it moves its torsos in line with 2-4 limbs who mark that sector and just doesn't cut under.  If you think hyper-jointed swivel hips I don't see it as a problem.  Rather I see some literally frightening kinetics.  

I mean if you go nature documentary, bug fights are boring, so give it the hip flexion and abductor,adductor control I'm talking about, as well as an almost serpentine ability to negotiate its upper and lower torsos, and the fights able to take on all comers better than a biped I'd reckon.  Give the spine the flexion associated with a fantastic scorpion tale.  Maybe an entomologist will say "but those things don't move like that" and you're response is this one does and cite the synergy between a humanoid gymnastically conditioned torso and the rest of an insect body with the same conditioning.  

For lair action type horror, give it pointy, piercing "feet" at the end of its legs.  It's fantasy, friend!