I'm lucky enough to have been gifted two Trout by a neighbour... and have not had the pleasure of preparing fresh fish before (or at least not unprepared fish).
I've attempted an internet search but haven't found a source that looks reliable to me.
Here is a a basic video tutorial so you can see the basic steps.
The biggest traps when cleaning fish is failing to remove all the guts, leaving bones in the filet, and not removing all the scales from the fish. You can, if you choose, just gut the fish and cook whole stuffed with some aromatics, which can be really good. This guy will show you how. This works very well with smaller fish like trout assuming your guests are used to it.
So to avoid the pitfalls mentioned above, you need to make sure that the cavity of the fish is fully empty before you start the filet. You also want to run your hand over the outside of the fish after your rinse of the cavity to make sure that all scales are gone. The best way to keep bones out is start at the spine and let the fishes rib cage guide your knife down and out. If you want to remove the skin (not recommended for trout but other fish have much tougher skins), just put the filet skin-side down and slide your knife along at a ten degree angle.
Oh, and the most important thing? Use a filet knife that is super sharp, you definately don't want to tackle cleaning with out a sharp knife.
Check that the fish is clean, and looks healthy. You should not need to clean the fish. If the fish is contaminated with something other than it's natural environment you may no want to eat it?
You generally need to fillet the fish to check it is clean and healthy (no parasites or worm trails). Leaving the fish whole and just gutting is OK, but generally the results are better when filleted
It is hard to describe the process. But consider that most fish have two fillets going from the tail, down the spine to the skull. Some fish anatomy pictures will help you understand what you are cutting over
Use a thin semi-flexible knife to separate the flesh from the frame (bones connected to spine). Start at the tail end (you hold the tail down on the cutting board), you can get your knife in from the top or bottom edge all the way in too touch the spine, and then smoothly run the knife along the top or bottom edge to the skull. The knife will always be just touching the spine
On the bottom edge stop just before the anus and divert over the rib cage (gut cavity)
To release the fillet, slice right behind the skull from top edge to bottom rib cage and the fillet should be detached from frame. Repeat for other side
You should now have two clean fillets, and a complete frame in one piece including tail, rib cage, guts, and head. This can be used as desired, or discarded
If the fish is releasing a lot of blood you are cutting to hard and have got into the spine or gut cavity. Go softly
To remove the skin find the weak spot of the flesh/skin connection on the corner that was over the rib cage. On some fish you should be able to grasp the skin with clean fingers and pull the skin back down the fillet to remove it. On other fish place the fillet skin side down on the board and run a thin sharp knife gently along the flesh/skin connection. Leaving a thin sliver of skin on is fine, as long as the outer layer of skin with the scales is removed
This takes plenty of practise to perfect. Watch a professional at the local fish shop to see how it is done. Or pay them to do it for you?
Removing the scales separately with a tool a is a old joke fishermen play on non-fishermen
Not proposing this as a definitive answer, but the following article gave me the confidence to try cleaning them
Rinse the outside of the fish.
While the fish is uncut, remove the scales. If you have a scaler you can use that, or you can go lightly with a grater or knife against the scales; or your fingernails in the direction of the scales (so you don't hurt yourself, but it'll take a while). Don't forget to scale the top and bottom (especially the stomach area- because that is the beginning point of the fillet) edges of the fish.
Then, slice from the fish's anus (a small hole right below the bottom fin) to the chin (up to the gills, bellyside of the fish) to create a fish pocket. Pull out ALL of the guts with your hands. The fish's meat is all stuck to the bones so you don't need to keep anything inside the fish. Some people use the guts, but most throw them out.
I prefer to keep the head on the fish (the eyes are delicious). Also I eat the fins and tail after frying, not sure if it's good for you or not but it tastes good (haha). Wash the fish off, rinsing it inside and out. Get rid of all the blood. You fillet it now, or just get cooking.
YouTube is a pretty good place to search for tutorial videos as well.