1. Explain it simply
除了 + noun + 以外 sets that noun aside, then the second clause talks about the rest.
除了 … 以外,都 means 'except X, all the others': 除了他以外,我们都去。
除了 … 以外,还/也 means 'besides X, also Y': 除了咖啡以外,他也喝茶。
2. Show examples
除了他以外,我们都去。
Chúle tā yǐwài, wǒmen dōu qù.
Except him, we all go.
都 = all the rest
除了苹果以外,我还想买香蕉。
Chúle píngguǒ yǐwài, wǒ hái xiǎng mǎi xiāngjiāo.
Besides apples, I also want to buy bananas.
还 = in addition
除了星期天以外,我每天都上班。
Chúle xīngqītiān yǐwài, wǒ měitiān dōu shàngbān.
Except Sunday, I go to work every day.
set one day aside
3. Share a tip
Keep the order 除了 + noun + 以外; the second clause always needs 都, 也, or 还.

