Mostly, if the keys aren't sticky, or malfunctioning, you only need
superficial cleaning. A bit of isopropanol (or alcohol-based sanitizer)
moistening a rag will dissolve most finger residues handily, just dampen
a cloth and wipe (it might take many strokes, or a few changes of cloth,
if the keyboard has lots o'gunk).
For debris under the key caps, it's sometimes useful to use a keycap puller
(can be fabricated with a little bit of music wire and some soldering/brazing skills, or purchased) and a vacuum in conjunction with a brush- 1/2" artists type is good- to loosen the bits. Wide keys have multiple
switch-like plungers, and/or wire braces, which complicates removal and replacement. If in doubt, take a picture of the keyboard before removal, so your keycaps go back in the right places.
Any shaft visible after removing the keycaps can be wiped with a cotton
swab damp with alcohol, if there's any sticking of that sliding part.
After a spill, sometimes (and ONLY for buckling spring types, the membrane
keyboards do NOT like liquids) a distilled-water soak is
You want to remove casing and cables before dipping.
Alcohol and tiny amounts of wetting agent (dishwasher rinse aid, Photo-Flo, Woolite, etc.) can be mixed in.