Make sure your work station is set up with proper lighting and some kind of magnification. I prefer a magnification headset. Tools include cleaning solution ( Hoppes, mineral oil, rust remover, WD -40 ), dental picks (plastic and metal ), old tee shirt cloth cut in small squares, Popsicle sticks, and acompressor with air adapter. Always wear safely glasses.
First, check the knife for any loose parts. Then, blow it our with your compressed air, gently. Use an an old tee-shirt square with a dab of Tri-flow on it and clean out the inside of the knife. Being careful not to get any grit and grim between the liners and the back springs. I will then work on the inside of the knife with a plastic dental tool to pick out any debris that is left or trapped.
Then, only if needed, use a bit of Hops gun cleaner to clean out any gunk. Check for rust and eliminate as much of the rust and corrosion as possible using a bit of WD-40/ rust remover on a tiny square of tee. Note: depending on scale material...be very careful not to get any of these solvents on your scales as this could damage or discolor them.
I am of the school of thought that patina is good. We wait years for it to develop on it own, some even force it. Other still, worship it. Some...not so much.
I therefore, do not recommend cleaning your knife any further than this. Although, some resort to using 00 steel wool on the inside of the knife and the surface of the blade. I normally do not.
If you must, because someone has badly scarred the knife through misuse and you just can't stand it, then sandpaper may be used. Start with 600 ( wet/dry) if the scares and abrasions are deep. Then use 800...then 1000, then 1500...then 2500. Start with the higher grade if the damage is minor.
I found one beauty that looked as if it was sharpened on the sidewalk or something. I was able to restore it with this method. Many use use a metal machined bar that is machined perfectly flat and wrap the sandpaper around this and work slowly and methodically at varying angles to achieve a mirror finish. Some strokes are made perpendicular to the blade, some length-wise. Others change the angle between each successive grade of paper until a mirror finish is achieved.
Finally oil all pivots and work the blades and sharpen her to a razors edge.
You are now the proud owner of a well cared for knife.