Alright, here's a quick guide I made of a few key things to memorize which will make combining runes easier.
"K shape":
There is only one option. All you gotta do is "ASK".
Blue rune (looks like "A"), Green rune (looks like "S"), "K" shaped wall rune.
"W shape":
Only works with another wall rune + the green rune.
Depending on the wall rune, gives 2 spell options.
"F shape":
Only works with another wall rune + either the green or blue rune.
Depending on the wall rune, green gives 2 spell options, blue gives 3 spell options.
"O shape"
Will always require the green rune, so click that second.
Then add your first (yellow) rune for Sigil of Death spell.
Or add your last (blue) rune to open a hidden door.
Or spell out S-O-L which is another name for the sun, gives healing, makes sense.
"Letter A with peak facing right-ish":
You can combine with either the 1st and 3rd, or the 2nd and 4th runes.
Or you can "trap the g": Yellow rune and "g" shaped wall rune.
or think "Secret Service": green "S" rune and "S" shaped wall rune.
"Upside down V shape (balancing a stick on top)":
Think of the shape as a scale... Place an apple (Red rune) on the scale,
it will either tip to the left (yellow rune to immediate left)
or it will tip to the right (green rune to immediate right)
Or forget the apple, and grab a blueberry (blue rune) and plum ("P" shaped wall rune).
If you see both "c" and "g" shaped wall runes, think "Coin Geyser" and try to associate with the red rune.
If you see both "P" and "A" shaped wall runes, think "Pale Ale" and try to associate with the yellow rune.