Every Day & Everyday
This mistake is again an easy one to make. Many children are taught incorrectly by teachers in elementary school that the word “everyday” means that something happens each day.
This is incorrect. The word “everyday” actually means common. When you want to talk about something that happens each day, you need “every day”.
“I eat an apple everyday every day to stay healthy.”
“My mother walks the dog in the forest everyday every day.”
You'll find that many native speakers also make the same and many other mistakes 
Myself included.
Your vs. You're
Its vs. It's
Affect vs. Effect
Who vs. Whom vs. Whose vs. Who's
Alot vs. A lot vs. Allot
Between vs. Among
just to name a few 
¡Hagámoslo ya!
For real Jeremi? That's a total relief. :D
Jeremi.Kress wrote:You'll find that many native speakers also make the same and many other mistakes :sweat_smile: Myself included.
Your vs. You're
Its vs. It's
Affect vs. Effect
Who vs. Whom vs. Whose vs. Who's
Alot vs. A lot vs. Allot
Between vs. Among
just to name a few :cry:
You missed "they're" and "their"! 
I'd like to point out that most of those aren't spoken errors, but written/typed errors. Spoken errors are more annoying to me. My most common mistakes in English probably have to do with inconsistent tense in a sentence, and inconsistent plurality.
Learning Italian every day!
Non-native speakers from Manila, Cebu, Mumbai and Bengaluru have the following spoken errors in common:
fails to use past tense - "Last night, I give him medicine."
uses present progressive instead of simple present - "Every weekend I'm visiting my grandma."
Prepositions - uses a limited set so there are usually many errors or inappropriate ones
mixes up "his" and "her"
Singular/plural - that's/those are, she's/they're
