Polishing it the art of rust bluing. Anyone can blue a piece of steel, though there is some skill in getting rust blue to a fairly high luster. The polishing, however is everything.
How do do it, depends on what it is. Many folks bluing a round barrel will chuck it in a lathe and have at it. Done wrong, looking at a low angle along the barrel will show waves in the finish after it is blued. If done right, reflected straight lines down the barrel will be appear straight. And there will be no waves.
I always polish my barrels, round or octagon, on the bench by hand, and work with hardwood backers or pieces of steel behind every piece of paper. (hard maple is ideal and won't mar the work if you slip - as a piece of steel will). Barrel polishing in this fashion is all unidirectional, but that's okay. Just takes longer in my experience. I often find that as I work along, I have to back up a grit or two because I didn't get a scratch from a courser grit completely polished out, but could not see that until I had gone on with finer grits. Check frequently by looking at the barrel at low angles with light out in front of you (a northern window is just about ideal for most lighting for this sort of thing).
When polishing I usually use WD40 for a lubricant. However, with courser grits something like Automatic Transmission Fluid works well too. But once you get to the finer grits, water is the only way to go in my experience ATF will basically prevent finer grits from cutting much of anything, and even WD40 will slow down the process.
Do not be cheap on abrasive papers. Change often, your fingers will thank you.
Polishing actions is another matter entirely. Switching the direction of the polishing by 90 degrees between different grades of abrasive is great. But be sure that the final grit, no matter how fine, is in line with the bore.
The problem with actions are all the strange angles, blind corners, concave and convex surfaces. Each action requires a unique sequence for polishing it best. How you go about requires experience, but each corner and line should be knife-edge sharp if possible and each blind corner needs to be polished all the way to where it meets the next surface. I have a photo or two that illustrates some of these problems but can't upload at the moment, unfortunately.
Some other things that help is to have a secondary set of screws if you are polishing parts that will mated together (e.g., the lower trigger bar and tang on an 85 Winchester. Another very helpful item is an old barrel stub to screw on to your action so you can hold it in a vice clamp easily. Holding the action well, is a big help in making polishing easy and relatively painless.
IF YOU USE YOUR FINAL BARREL WHILE POLISHING THE ACTION YOU WILL REGRET IT. The caps are there for a reason