Brass hardware requires very little maintenance. 

Warm water and a soft cloth are all that are required to clean spillages or remove residue from your handles. 

If you spill anything acidic on your hardware and don't clean it immediately it will etch through the surface coating and leave a bright mark. You should attend to problems as they arise with warm water, a PH neutral soap can be applied if required.

Do not use any scouring or abrasive pads / cloths to clean your hardware, they will mark the surface. 

Do not use any household bleach or cleaning products on the hardware. Brass is naturally self cleaning in terms of bacteria resistance and this was the main reason for use in hospitals in the Victorian era (lots of interesting info can be found online.)