Generally...
The lochs seems more affected by the weather than anywhere else I have fished. The fishing can be dire!
You won't see much hatching.
The fish want big flies even in a fairly small ripple, sizes 8 and 10 being my go to sizes.
No water is too shallow to hold fish.
The dour lochs can be very dour indeed. If you are only there for a week do you want to spend a whole day flogging away for the
chance of a good fish? Dun Murchaidh is the least scenic loch between Barra and the Butt of Lewis!
Take the advice of the guide books with a pinch of salt, I have had good weeks without ever fishing any of the recommended lochs. Some of the unregarded little puddles can give you fish of 2lb or more.
The further you are from the road the better the fishing
If you intend walking about in the wilds take some foam rubber pipe lagging to help you cross the many barbed wire fences unscathed.
Enjoy
Andy