I bought a book last year called An Introduction to Egyptian Hieroglyphics.
Very interesting.
Hieroglyphics were long thought to be 'picture-writing', but they're not. Some are inspired by pictorial representations, e.g. the Egyptian hieroglyph for 'r' is a mouth, and the Egyptian word for mouth starts with an r sound. At least one hieroglyph is onomatopoeic - the hieroglyph for 'f' is a snake. And a snake's hissing does sound a bit like the f sound, pretty neat, huh?
Hieroglyphs actually represent one, two or three consonants. Plus, some hieroglyphs are used as determinatives. These determinatives have no sound but reinforce other hieroglyphs.
Here are the hieroglyphs of one consonant:
Common hieroglyphs of two consonants:
Common hieroglyphs of three consonants:
Common hieroglyph determinatives: