With Solvol Autosol/Brasso and fine steel wool. DO NOT use a nylon pad or abrasives, this will damage the chrome. Steel wool however is softer than chrome so you will not touch the chrome, just the rust. NB if it's not too bad a cotton rag and polish will do it, but it's slower.
Classic car/bike enthusiasts have been doing this for years. :-)
Don't try this on ally rims BTW. Actually you can, I have, but it only ever gives a dull shine. OK if you like a dull shine...