Good double action work starts with proper fitting grips. The standard size magna style grips on a J frame do not lend themselves to good DA work for most hand sized. You want a grip that fills your hand to prevent gun movement under the recoil of repeat shots, and allows for a straight rearword trigger pull. Some go with custom grips, some use stock grips along with a Tyler T type adaptor. You have to experiment and see what best fits your hand.
A smooth, polished, non-serrated trigger helps as well. I do my best DA work by placing the first joint of my trigger finger on the trigger. A smooth, steady trigger pull works best for me, though I know some shooters who like to stage their pull, completing most of the pull, then stoping, and squeezing off the rest until release. This works best with a trigger pull that stacks, like on the older Colt revolvers, and is really not a good method for combat shooting.
Smith J frames tend to be a little stiffer in their pull compared to K, L, and N frames. An action job, along with a slightly reduced main coil spring (as long as it does not comprimise reliability) can make a big difference, as can a lot of DA practice. DA shooting has almost become a lost art now that so many have switched to semi's.
Larry