If your clarinet or other instrument has silver plated keys, one of the biggest issues is keeping tarnish from returning after painstakingly polishing.
Although it is very difficult to entirely prevent silver from oxidizing, you can help reduce re-tarnish with 3M Anti-Tarnish Strips.
These are not expensive and last quite a while. All you have to do is toss a strip in your instrument case.
They can be found for $4.44 for a 5-pack from Walmart.com: