This is the method I use to clean and prepare a chromed steel rim, If you have a better way or have had an experience that may help please post your constructive comments.
Start out by inspecting the rim. See if there are any cracks or deep rust pits.
If this is all good I start by removing the rim tape. The rim tape is usually a ring of rubber that protects the tube from any sharp sections on the nipples or spoke ends. The rim tape can also be insulation tape wrapped around the rim a few times. In my case the last person to service the rim used masking tape. Masking tape is not the best product to use as it disintegrates into a gooey mess. It also looks like it trapped water between itself and the rim making the chrome flake off and the corrosion begin.
Ji