Softbodies were not designed to do clothing, but there have been a few who have found moderate success when applying it that way.
The trick is to create a vertex group (usually called SOFTGOAL or something like it) which indicates how much power the softbody engine has over the mesh. 1.0 (red) means that the vertex is controlled exclusively by the armature/constraints/whatever, and 0.0 (dark blue) means that the vertex is manipulated exclusively by the softbody engine.
Recognize what parts of your clothing should be free to wobble and flap and what parts should not. Weight Paint the SOFTGOAL to blend in and out of each region.
Remember also that softbodies do not handle collision particularly well, especially when dealing with deformable objects. So you still can’t do things like capes and dresses with softbodies alone: they need some additional help from an armature or some other constraint.
Hope this helps.