I fish a slower warm water river just down the street from me. I am also a big fan of Joe Humpreys. I'm not sure if it's because I learned to fish from Ian James on my home river before I tackled cold water trout rivers or not, but the techniques are very similar. Warm water offers far less top water action however, so you need to really concentrate on the nymphing if you want to get anywhere. Joe is, without a doubt, one of the best. He does just as well on the water here as he does on his home streams. I know the fellow who was pared with Joe on a one fly contest up here a few years back. That fellow got his butt kicked HUGE.
A good part of the time I use upstream nymphing techniques. Check out Joe's nymping video. The only thing is the bottom of this river isn't as friendly as the trout streams I fish. I loose a lot of flies. Also know your fish species. Carp are really not that diffent than going for trout when nothing in rising. Small nymphs and cray fish patterns work the best. Caddis and midges dominate the river here. SM bass will go after nymphs, streamers and crayfish. Poppers on top work too, but you need to know WHERE and when to use them. My favorite flies for Bass are Muddlers of various types, Puke flies and crayfish...but I also fish nymphs for them. My largest river bass to date was a SM on a #16 midge larva.
Last but not least, you have to keep trying and give up on the cute little trout dries. If a bass is going to hit a dead drifted dry, it's going to be big like a grasshopper, cricket, or hex. If you have a good hatch of those it's a good time for dry fly action.
You need to find out what species is in your river then start from there. ...and a good fly to start with is a good ol Olive (or black) Woolly Bugger. It's the one fly choice for most, "I don't know what to do?" situations.