Soft jerkbaits, referred to as "flukes" by most bass anglers, are often thought of as a summertime bait. But I've found soft jerkbaits to be highly effective in the fall, even into fairly late fall.
For river smallmouth bass, I like to use a full sized (5-inch) soft jerkbait. Typically I nose hook the fluke with an octopus-style hook, the kind often used when fishing live bait. The areas I target are often quiet close-to-shore pockets, where smallmouth bass can dart out into the faster current to ambush prey.
There's not a lot to the presentation, which is part of the magic. Simply make casts into these pockets, getting as close to shore as possible. Then employ a retrieve that borders on dead-sticking. Just let the bait slowly sink, giving it an occasional twitch to give it that wounded minnow look. Reel in the resulting slack. After a few such twitches — if a big river smallie hasn't sucked in the lure — it will likely be out of the high percentage area. Quickly reel it in and cast again. While bronzebacks sometime crush the soft stickbait, often times then just draw it in. You'll just feel a tightening of the line, the signal to impart a strong, sweeping hookset.
On lake and reservoirs, ones that feature submerged vegetation, I often use a smaller soft jerkbait, one in the 3.5- to 4-inch range, on a drop shot rig, again nose hooked with an open live-bait style hook. It's an ideal rig for pitching back into pockets of remaining green weeds, and a nice change-up for times when a bulkier presentation, like a flippin jig-pig combo, isn't doing it.
The drop shot/soft jerkbait combo is effective on both smallmouth and largemouth.