Re: What do you throw?
I've only been flyfishing for 3 years, so you might want to take this with a grain of salt. However, probably 90% of my fishing has been from a tube on a lake.
In general, depth is the key. Then size, then shape, and finally color. From the scenario you gave, it's probable that you weren't fishing deep enough. You can either add weight (split shot, tungsten beadheads, sink tip/sink line), or countdown your offerings deeper, and strip slower with longer pauses. The problem with that is that you can come up empty anyway if the fish want a faster moving fly.
You can also make your own 'sink tip' with T-heads, a tungsten impregnated length of line you can cut to length and add loops to, then attach to your regular floating line. It won't cast as well as a true sink tip, but you can still cast 50-60 ft and costs a fraction of a full sink/tip line. However you decide to go, a weighted presentation will allow you to work your fly faster, while staying at the right depth.
Another method popular here is the indicator presentation, or as we call it in AZ, the Ferry Rig. Apparently they invented this rig at Lee's Ferry, or it's where the rig became famous. Whatever. This involves using a 9 ft. leader, with about 2 ft. of tippet (note: if it's pretty windy you may want to add a second 2 ft. tippet section to allow for vertical drag). Add a split shot (I tend to use a BB) just above or below the leader/tippet knot. Add a thingamabobber at the top of the leader. Add a press on foam indicator about 12 inches below the TMBobber (sometimes the strikes are so subtle hat the big indicator never moves). As soon as you see the smaller indicator move, set the hook and try to set off to one side. If this thing comes back at you, you're in for a fun, possibly painful, tedious time.
The idea here is to "fish the odds." Trout seem to spend a large percentage of the time in and around 10 ft. in many lakes, patrolling their little domain. You fish this rig at the 10 ft. depth, and drift along with the wind/current.
Now here's the negatives to that rig. It tangles easily, either when casting or when a fish starting rolling around on it. It's a pain to cast. Lifting this thing out of the water from a tube is . . . fun. Plan on either very short casts or basically no cast. And it can be boring. After all, this is essentially bobber fishing. Throw it out and watch it. For. A. Long. Time. Finally netting your catch can be a pain, as your total length of leader to fly can be over 14 ft. So take a long rod. If you haven't guessed, I hate this rig.
All that said, this thing works. And sometimes it outfishes any other rig/fly/system I've ever seen or fished. Whatever. The point is, it catches fish when pretty much everything else strikes out, regardless of drawbacks. The only thing that has to happen with this thing, is the weight has to touch bottom.
Flies to fish with the FR: almost anything, but my favorites are prince nymphs (any nymph will do, but I've had the most success with #14 PNs), simiseal leeches, small bunny leeches, SJ worms, zebra midges, and my personal fav, the Rickard's nymph.
Don't like any of those ideas? Tie on a hopper and fish any shade you can find. Fish it like a popper; short, sharp strips. You won't outfish your partner every time, but the fish you catch will be more exciting, I guarantee it.
Hope that helps.
"Three-fourths of the Earth's surface is water, and one-fourth is land. It is quite clear that the good Lord intended us to spend triple the amount of time fishing as taking care of the lawn." ~Chuck Clark