Перед собеседованием я ещё раз открыла резюме и исправила одну ошибку.

Because the preposition перед normally requires the instrumental case.

So:

• собеседование = interview
• перед собеседованием = before the interview

This is a very common pattern:

• перед уроком = before the lesson
• перед встречей = before the meeting
• перед экзаменом = before the exam

In this sentence, перед собеседованием gives the time setting: before the interview.

Yes, you often can, but there is a slight difference in feel.

• перед собеседованием = right before the interview / in the time leading up to it
• до собеседования = before the interview, more neutrally or more broadly

In this sentence, перед собеседованием sounds very natural because the person looked at the résumé and fixed a mistake shortly before the interview.

So both are possible, but перед собеседованием fits the context especially well.

Because the sentence describes completed actions.

Russian often uses:

• perfective aspect for a completed, result-focused action
• imperfective aspect for a process, repeated action, or background action

Here:

• открыла = opened
• исправила = corrected/fixed

The speaker did these things once, and the actions were completed. That is why perfective verbs are used:

• открыть → открыла
• исправить → исправила

If you said открывала or исправляла, it would sound more like you are describing the process, repetition, or an unfinished/background action.

That is the past tense feminine singular ending.

In Russian past tense, the verb agrees with the gender and number of the subject:

• masculine: открыл
• feminine: открыла
• neuter: открыло
• plural: открыли

So я открыла tells us the speaker is female.

The same is true for исправила.

If a male speaker said this sentence, it would be:

Перед собеседованием я ещё раз открыл резюме и исправил одну ошибку.

Yes, Russian often omits subject pronouns when they are clear from the verb form.

So this sentence could also be:

Перед собеседованием ещё раз открыла резюме и исправила одну ошибку.

That still sounds natural, especially in conversation, because открыла and исправила already show a feminine I.

But including я is also completely normal. It can make the sentence a little clearer or slightly more explicit.

Ещё раз means once again or one more time.

So:

• я ещё раз открыла резюме = I opened the résumé once again / one more time

It suggests the speaker had already looked at it before and decided to check it again.

This expression is extremely common:

• Повторите ещё раз. = Repeat it one more time.
• Я прочитал это ещё раз. = I read it again.

Yes, often you can.

• ещё раз = one more time
• снова = again

In many contexts they are close in meaning. But ещё раз emphasizes the idea of another repetition, while снова is a bit more general.

So:

• я ещё раз открыла резюме = I opened the résumé one more time
• я снова открыла резюме = I opened the résumé again

In this sentence, ещё раз sounds especially natural because checking a résumé again before an interview is a deliberate repeated action.

Because резюме is one of those Russian nouns that are usually indeclinable.

That means the form stays the same in different cases:

• резюме
• открыла резюме
• в резюме
• без резюме

Even though the case changes in meaning, the word itself does not change form.

This is common with some borrowed words in Russian.

Because ошибка is a feminine noun, and one must agree with it in gender and case.

Base forms:

• один = masculine
• одна = feminine
• одно = neuter

But here the phrase is the direct object of исправила, so it is in the accusative case:

• nominative: одна ошибка
• accusative: одну ошибку

So:

• одну agrees with the feminine noun
• ошибку is the accusative form of ошибка

Because it is the direct object of the verb исправила.

The speaker corrected what?
→ одну ошибку

In Russian, the direct object often goes in the accusative case.

Compare:

• Я вижу ошибку. = I see a mistake.
• Я исправила ошибку. = I corrected a mistake.
• Я нашла ошибку. = I found a mistake.

So ошибка changes to ошибку because it is the thing being corrected.

Because и is simply joining two verbs with the same subject:

• открыла
• исправила

This is a normal compound predicate:

я ещё раз открыла резюме и исправила одну ошибку

There is no need for a comma because it is one clause with one subject doing two actions.

No, Russian word order is fairly flexible, though some orders sound more natural than others.

This version is very natural:

Перед собеседованием я ещё раз открыла резюме и исправила одну ошибку.

It starts with the time expression Перед собеседованием, which sets the scene first.

You could also hear variations like:

• Я перед собеседованием ещё раз открыла резюме и исправила одну ошибку.
• Я ещё раз открыла резюме перед собеседованием и исправила одну ошибку.

But the original order sounds smooth and neutral.

Yes, it is completely normal.

In Russian, открыть is commonly used for opening:

• a file
• a document
• a webpage
• a letter
• a résumé

So открыла резюме can mean she opened the résumé on a computer or simply brought it up to look at it again. It sounds very natural in modern Russian.