Check for insects in the water, evidence of hatches. Do your best to locate shoals, have a look for any feeder streams too. If you see rises, try to figure out if they are feeding under the surface, juuuust under the surface, or on top. If you can see insects in the water, try to match what it is, and concentrate around shoals, submerged islands or other features that you can make out. On some lakes its pretty hard but most "good' lakes will have visible shoals and will be fairly shallow in at least SOME parts. Try to present the fly where you think the fish are feeding, depthwise. The first fish you catch, pump its stomach to see what its eating, and you'll know what most will come on. Changing weather is bad...overcast ,as long as it is stable, is great. Sunny days, rainy days, they can all be great ....it really depends on stability. Crazy barometer can wreak havoc on it too, IMO. Some people don't buy it but it kinda goes hand in hand with weather shifts. If I'm having a hard time getting the first fish i'll throw on a maroon colored microleech and drag it on the dropoffs, usually I'll get at least one like that, then pump it (if i have a pump handy!).
I dunno....I get skunked as much as the next guy....and to be honest, much of what I have learned has been passed on info.....so probably, the best advice? If you see somebody camping, or fishing, just ask how the fishing has been. Most guys are happy to gloat and share, except the grumpy ones, in which case, it will be a short conversation and wont take much of your time anyways. Good luck with it you sound very enthusiastic!