A veces olvido la tilde, sobre todo cuando escribo deprisa en el móvil.

A veces is a fixed expression meaning sometimes.

• A veces = sometimes
• Algunas veces = sometimes / some times, also possible but a bit more explicit or heavier
• A la veces is incorrect

So A veces olvido... is a very natural way to begin the sentence.

In Spanish, subject pronouns are often omitted because the verb ending already shows who the subject is.

• olvido = I forget
• escribo = I write

So A veces olvido... already clearly means Sometimes I forget... without needing yo.

You could say Yo a veces olvido la tilde if you wanted extra emphasis, but normally it is not necessary.

Both forms exist, but they are used differently.

• olvidar algo = to forget something
  
  • Olvido la tilde = I forget the accent mark
• olvidarse de algo = to forget something
  
  • Me olvido de la tilde

In this sentence, olvido la tilde is a straightforward transitive structure: verb + direct object.

For learners, it is useful to remember:

• Olvido la tilde
• Me olvido de la tilde

Both can be heard, but the version in your sentence is very standard and simple.

Here la tilde means the written accent mark used in Spanish spelling, for example:

• móvil
• rápido
• inglés

So it is not talking about pronunciation in general, but about the little written mark over the vowel.

In everyday Spanish, tilde is the normal word people use for that accent mark.

Spanish often uses the singular to talk about something in a general way.

So olvido la tilde means something like:

• I forget the accent mark
• I forget to add the accent mark

It does not mean there is only one specific accent mark in the world. It is a general reference to that kind of spelling mark.

This is very natural in Spanish.

Sobre todo means especially, above all, or particularly.

In this sentence:

• A veces olvido la tilde, sobre todo cuando...
• Sometimes I forget the accent mark, especially when...

It introduces the main situation in which the problem happens.

Very common examples:

• Me gusta la fruta, sobre todo las fresas.
  I like fruit, especially strawberries.
• Estoy cansado, sobre todo por las mañanas.
  I’m tired, especially in the mornings.

Because this sentence describes a habitual, real situation, not a future or uncertain one.

• cuando escribo deprisa = when I write quickly
• this refers to something that really happens, regularly

Spanish uses the present indicative after cuando for repeated or general actions.

If you were talking about the future, Spanish would normally use the subjunctive:

• Cuando escriba en el móvil, intentaré fijarme más.
  When I write on my phone, I’ll try to pay more attention.

So in your sentence, escribo is correct because it describes a usual pattern.

Both can mean quickly, but deprisa is very common in everyday speech and often feels more natural in casual contexts.

• escribo deprisa = I write quickly / in a hurry
• escribo rápidamente = I write quickly

A small nuance:

• deprisa often suggests doing something fast, maybe a bit hurriedly
• rápidamente can sound slightly more neutral or formal

In this sentence, deprisa fits very well because typing on a phone quickly often suggests haste.

Sometimes learners try to translate directly from English and say escribo rápido. You may hear that in informal Spanish, and many native speakers do say it, but for learners it is safer to use:

• escribo deprisa
• escribo rápidamente

Those are clearly standard choices.

So in this sentence, deprisa is an excellent option.

En el móvil is very natural in Spain when talking about writing or doing something on your phone.

• escribir en el móvil = to write on your phone

Why el and not mi?

Because Spanish often uses the definite article when the object is obvious from context. If I am talking about my own habits, el móvil will usually be understood as my phone.

You could also say:

• cuando escribo en mi móvil

That is correct too, but slightly more explicit.

Con el móvil usually means with the phone, focusing more on the device as an instrument, not necessarily the screen or typing interface.

Yes, móvil is the normal word in Spain for mobile phone / cell phone.

In many parts of Latin America, people more often say:

• celular
• sometimes móvil, depending on the country

So if you are learning Spanish from Spain, el móvil is exactly the right choice.

Because Spanish spelling rules require an accent mark there.

móvil is stressed on the first syllable: MÓ-vil.
Words ending in -n, -s, or a vowel are normally stressed on the second-to-last syllable. Since móvil does not follow that default pattern, it needs a written accent mark.

This is actually a nice detail in the sentence: the speaker says they forget the tilde, and the word móvil contains one.

The comma separates the main statement from an added comment:

• A veces olvido la tilde
• sobre todo cuando escribo deprisa en el móvil

The second part adds extra information: it tells us when this happens most often.

The comma is natural here because sobre todo introduces a kind of afterthought or clarification.

You may sometimes see similar sentences without a comma in less careful writing, but with the comma it is clearer and more polished.

Yes. Spanish allows some flexibility, although the original version is very natural.

For example:

• Olvido la tilde a veces, sobre todo cuando escribo deprisa en el móvil.
• Sobre todo cuando escribo deprisa en el móvil, a veces olvido la tilde.

But the original:

• A veces olvido la tilde, sobre todo cuando escribo deprisa en el móvil.

sounds very natural and straightforward.

It starts with the general idea sometimes, then explains the main situation where it happens.

It is mostly neutral everyday Spanish.

Nothing in it is slangy or unusually formal.

• A veces = normal
• olvido = normal
• la tilde = normal
• sobre todo = normal
• deprisa = common everyday word
• el móvil = standard Spain Spanish

So this is the kind of sentence you could say naturally in conversation or write in an informal message.