Simple method 1: get a cloth and glass cleaner and wipe the surface of the keys. Pretty effective most of the time.

Simple method 2: get a compressed air spray and use it to clean the dust accumulated between the keys.

Complicated method 1: special for liquid spills. Buy a new keyboard (yes, even if it's a laptop, they sell that part for replacement), watch a youtube video on how to disassemble your particular model of laptop and go for it. With patience and care you will be able to replace the keyboard and it will be as good as new.