Learn Hardcore Spanish (Spain): Me levanto antes que mi hermana.

No. The subject is “yo” (even if it’s not written).
The “me” is a reflexive pronoun that shows the action comes back to the same person who does it.

(Yo) me levanto. → I (subject) get myself up (object = me).

Spanish needs this pronoun with reflexive verbs like levantarse, vestirse, ducharse, sentarse, etc.
English often doesn’t show it (you usually don’t say “I get myself up” — just “I get up”), but Spanish must keep me / te / se / nos / os / se.

Can I also say “Yo me levanto antes que mi hermana”?

Yes. That’s perfectly correct.

Me levanto antes que mi hermana.
Yo me levanto antes que mi hermana.

Both mean the same thing.
Adding “yo” just adds a bit of emphasis on I (as opposed to someone else):

Yo me levanto antes que mi hermana, pero ella se acuesta más tarde.
I get up earlier than my sister, but she goes to bed later.

Why is it “antes que” and not “antes de” here?

Because it’s a comparison between two people doing the same action.

In standard grammar:

Use antes que when you’re comparing subjects / people:
- Me levanto antes que mi hermana.
  I get up earlier than my sister.
- Sale antes que yo.
  He leaves earlier than me.
Use antes de for time / moments / infinitives:
- Antes de las ocho. – Before eight o’clock.
- Antes de salir. – Before leaving.

In real life, many native speakers do say “antes de mi hermana”, but “antes que mi hermana” is the more careful, recommended form for this kind of comparison.

So is “Me levanto antes de mi hermana” wrong?

It’s very common in speech and most people will understand it without a problem. Many natives say it.

However, in careful / formal Spanish, for comparing when two people do the same action, “antes que” is preferred:

Recommended: Me levanto antes que mi hermana.
Very common but less recommended in grammar books: Me levanto antes de mi hermana.

If you’re studying “correct” or exam Spanish, use antes que here.

What is the difference between “mi” and “mí”, and why is it “mi hermana” without an accent?

mi (no accent) = my, a possessive adjective:
- mi hermana – my sister
- mi casa – my house
mí (with accent) = me, a stressed pronoun used after prepositions:
- para mí – for me
- sin mí – without me

In “mi hermana” you are saying “my sister”, so you need mi (no accent).

Can I change the word order, like “Antes que mi hermana, me levanto”?

Yes, that’s correct, just less typical for this simple sentence.

Possible orders:

Me levanto antes que mi hermana. (most natural)
Antes que mi hermana, me levanto. (correct, a bit more literary/emphatic)
Yo me levanto antes que mi hermana. (adds emphasis on I)
Me levanto yo antes que mi hermana. (strong emphasis on I vs. others)

Word order is fairly flexible in Spanish, but the original order is the most neutral and common here.

What’s the difference between “me despierto” and “me levanto”?

Me despierto = I wake up (I stop sleeping, but I might still be in bed).
Me levanto = I get up (I physically get out of bed / stand up).

Example daily routine:

Me despierto a las siete, pero me levanto a las siete y cuarto.
I wake up at 7, but I get up at 7:15.

In your sentence, “Me levanto antes que mi hermana” is about the act of getting up, not just waking up.

Could I replace “mi hermana” with a pronoun and say “Me levanto antes que ella”?

Yes.

Me levanto antes que mi hermana. – I get up earlier than my sister.
Me levanto antes que ella. – I get up earlier than her.

Both are fine. Use mi hermana if you’re introducing who she is, and ella if it’s already clear from context who you’re talking about.

Why is it “mi hermana” and not “la mi hermana” like in some other languages?

In Spanish, you don’t normally put an article (el, la, los, las) before a possessive adjective (mi, tu, su, nuestro…) in this kind of phrase.

Correct:

mi hermana – my sister
mi padre – my father
mis amigos – my friends

Incorrect in standard Spanish:

✗ la mi hermana
✗ el mi padre

So “Me levanto antes que mi hermana” uses the normal pattern: mi + noun, without an article.