mMes matins

Parce quComme je suis une [élève/étudiante ?], je me reéveille à 5 h 30 du matin, avant dule lever du soleil, quand le ciel est encore noir.sombre,

"parce que" is used to connect two independent clauses ; in order to start a relative clause, you're spoilt for choice => comme, puisque, vu que, étant donné que...

"étudiant" only applies to higher education students; if you're a high schooler, you're "une élève", or even better, "une lycéenne"

Space before and after "h" when it means "heure(s)"

avant + nom (although we do say "avant DE faire quelque chose" to connect the preposition and the infinitive verb)

We rather say that the sky is "sombre"

Eet puis, je preépare mon petit-déjeuner.

It's way better not to separate "et puis" from the previous sentence with a period (this one works a bit like "parce que"), unless you truly know what you're doing and want to give the sentence some kind of stylistic effect

D'habitude, je preéfère le frappeé aux fruits, le yaourt, ouet le muesli (granola ?).

"le frappé, le yaourt ou le muesli" would mean one of these things alone excluding the others, but I assume all those are part of what you prefer

"Muesli" and "granola" both are cereal mixes but with different ingredients; since I don't know what you have for breakfast, I can't tell

Quand j'étais petite, je mangeais seulement deu porridge avec des fruits tous les jours.

Indefinite quantity of something uncountable = de+[article] => DU porridge, DE L'eau, DU vin, DU sable...
Indefinite quantity of something countable = des => DES enfants, DES fruits, DES vases, DES chiens...
(remember some uncountable English nouns are countable in French and the other way around)

Après ça, je m'habille.

"ensuite" or just "après" both are way more natural than "après ça"

Une jour, je me souviendrai de vérifier la météo avant de choisir ma tenue, mais pas aujourd'hui.

SE souvenir DE quelque chose

Dans tous lla plupart des cas, même si je me reéveille à 6 h ou 5 h, d'habitude, je suis en retard.

If you usually are late, then it's in most cases => dans la plupart des cas

Mon bus arrive à 6 h 45 mais parfois, je dois courir pour celal'attraper.

"pour cela" would mean you have to run for the bus to arrive, but you have to run to catch it, logically

J'èespeère que mes camarades de classe ne me voient jamais moi quand je cours pourderrière lae bus.

<e> in front of <s> combinations (<ss>, <st>, <sp> etc) is automatically pronounced /e/ so you don't need any accent => espère

Simple (unstressed) direct object pronouns = me, te, lui/la, nous, vous, eux/elles => ne ME voient ("j'espère qu'ils ne me voient pas moi" would mean "I hope they don't see ME but someone else")

Peut-être que si je preéparais mon sac la nuit dernierveille au soir, je ne serais pas en retard.

"peut-être" starting a clause = peut-être QUE

"la nuit dernière" is only understandable from the enunciative context of the day referred as "today", so it would only mean on the 19th of May, since "today" is the 20th
the night before = la veille au soir (the period between 5pm and late in the night is typically called "le soir")

Ok, c'esVoilà à quoi ressemblent tous mes matins !

I'm not sure I completely grasped this one. If you meant something like "well, here's how all my mornings look like", you can phrase it like this