Can I ask, what kind of fly line are you using, i.e. Floating, Intermediate, Slow Sink, Sink Tip, etc.?
If you are seeing fish movements on the surface then I'd use a floating line and two or three flies - a dry fly at the top and nymphs below. Cast and leave or twitch sporadically to give the bob fly (top dropper) a little 'kick' to give it life - the nymphs, of course, will follow suit out of view.
Remember, none of these imitated insects move fast through the water so you can afford to cast and wait a minute as the nymphs sink and search deeper water. Then tickle in a few feet - this will draw the nymphs up towards the surface - and let them sink awhile again.
If there's a hatch on and a bit of wind try a large, single dry fly with floatant and strip it back across the waves with a bit of speed to make a small wake. In this case pattern isn't as important as silhouette , disturbance and speed of retrieve as you are appealing to a trout's attack instinct rather than seducing a selectively feeding, even fixated fish.
If you want to identify the 'flies of the day' walk to the windward shore and look amongst the rocks at the water's edge. If there's a good hatch on you may see hundreds of spent or drowned insects - look closely and pick a fly from your box to 'match the hatch'.
Gently lift a few stones from the edge and look underneath for any nymphs or crustaceans. This can help give an idea of likely trout food when you can't see insects on the surface. I'll always do this when fishing new water.
Hope there's something useful for you there.