The bleach bath works really well on silver. It is my understanding that it will destroy coppers and won't do anything to the newer alloy halfs and dollars. (post 64 Kennedy halfs and the Eisenhower dollars).
First clean the coins well to get an even coloration. If you have a bunch of oils from your hands on them, it can get a little bit of a tie-dye look to it. This can be done with regular hand soap or dish soap. If there is a bit of color on them already, (you get them from a coin shop, they won't be cleaned as collector's don't generally mess with their coins) try toothpaste or soaking them in coke for a little while to get the old color off.
Once they are as clean as you want them to be for an even coloring, I use a 50/50 mix of bleach and water and let the coins soak for 10-15 minutes turning them over half way. I assume that if you want them darker, you can let them set longer, but I wouldn't do it overnight or anything, as it is a chemical reaction and can eat your coins given a long enough time to work on them.
Then just buff off with one of those nail file blocks like Bungee says above. You will destroy the file by coating it coppery looking metal, so don't borrow your wife's/girlfriend's as she will not be happy with you. Try to be gentle with the filing and use as smooth a file as you can, because you are removing metal, and you don't want to scrub off too much.
I agree that shiny is good, but I like a bit of color, as it makes the design on the coin pop. If you polish when you're done, the coin will reflect plenty of light and have a visible design when you're handling it.