Soloing a thief, tricky with any build but skills you have do depend on the path build you choose.

Hide and Backstab are your bread and butter for soloing, some mobs wont see you hiding if you need to flee and rest. It is much safer to solo where you can hide! You need to dish out damage fast too. If your chosen path doesn't include some sort of damage skill. Choose knife if you have the points. If not choose the kick skill.

I like to hunt mobs near healers that you can barter armors for healing. Also, a strong mercenary can rescued you, and I imagine circle stab could be effective.