First, de-scale. Don’t bother with a de-scaler, your own hands or the blunt side of a knife work well.
Then, open each fish from asshole to right under the mouth. Again, with most fishes you can do this without any tools if you’ve got healthy nails. Take out the guts. Rinse for a second (don’t drown the fish, it’s dead and gutted already). Except for some specially-sadistic fishes such as catfish or red mullet, the bones are all either forming the fins or sprouting from the spine: the “back” of the fish has bones all along; the “front” has a row of bones from tail to ass and two rows (the bones in these may be softer) surrounding the abdominal cavity. Stick one nail between the bones and meat (the meaty part of the finger faces the meat of the fish) and move it along to separate them. Rip one on side one, bottom fish; rip two on side one, top/back of fish; turn fish around, rip rip. Break the spine at each end once it’s separated from the meat. Toss it away. Takes a lot less time to do it than to explain it: if it didn’t, my family wouldn’t have had the tons of anchovies I’ve cleaned!
Also, give flat fishes a try: those don’t even need to be gutted, both the length-wise fins and the bones come off very cleanly once cooked. The fins are usually cut off somewhat to make the fish less bulky and thus easier to fit into the pan. In general, “dark” fishes such as anchovies or herring need more cleaning than “white” ones such as cod or flat fishes, and the smaller the fish, the worst it is to clean.