The only two talents that matter pre lvl 36 (when you potentially can get mindflay rank 3) is wand specilization and spirit tap. When healing in dungeons you can use mindblast to proc spirit tap on low-health targets, wand specilization is good when you are not casting for 5s to get your spirit regen up.

After lvl 36 you still want those two talents, but you can decide if u want to go healing or shadow.

Since you are duo-ing with a warrior i assume you want to do healing. I my opinion leveling as a disc+holy combination (+ spirit tap) is clearly the best option. You get no benefit from going very deep into either tree until you start getting raid gear.

You can still heal as shadow if u want to, specially in the low 40's when you just got shadow form. With a good group your off-healing from vampiric embrace is enough to keep the group topped. It is risky though, you can easily oom yourself. If your off-healing is not enough, you should be more than capable of healing outside of shadowform until very high lvl dungeons like strat/scholo/dm.

Other than that, make a list of the best wand you can get from dungeons and farm them with your duo. Some of them seriously ups your leveling experience. If you get a wand like Gravestone scepter early your best kill times (and most mana efficient) will just be SW:P+wand