매일 vs 맨날 vs 일상
I've seen all these words translated into "everyday".

I've found 맨날 is more informal than the other two, but is 일상 ever used/should it be used?

Would 저는 매일 연습해요 and 저는 일상 연습 해요 mean the same thing?

Question

매일 vs 맨날 vs 일상
I've seen all these words translated into "everyday".

I've found 맨날 is more informal than the other two, but is 일상 ever used/should it be used?

Would 저는 매일 연습해요 and 저는 일상 연습 해요 mean the same thing?

Answer

메일 (adverb, sometimes noun) = every day (매 = every, 일 = day. most widely used, standard term).
맨날 (adv) = same as 매일, but very informal (맨 = every, 날 = day).
일상 (noun) = formal term for "daily routine/situation" (일 = day, 상 = usual state). 
일상적(이다) (adj) = daily; everyday.  그 시절에는 전기가 끊기는 것이 일상적이었다 (In those days, power outage was a daily thing).
일상적으로 (adv) = daily, usually, constantly.  그 당시에는 전기가 일상적으로 끊겼다 (In those days, power went out constantly).

일상적이다, 일상적으로 are less specific and more formal than 매일.  매일, 맨날 are preferred in conversation.

"저는 일상 연습해요" is wrong.  You can say "저는 일상적으로 연습해요" or "저는 연습하는 게(것이) 일상적이에요" (Practicing is a daily thing for me), but these can sound a little too vague and formal.

Answer

맨날 can also mean "always".