La profesora nos pidió que escribiéramos el título en la primera hoja y dejáramos margen a la izquierda.

Because pedir que is a structure that normally triggers the subjunctive when one person asks another person to do something.

Here, la profesora asked us to do something, so Spanish uses:

• pidió que escribiéramos...
• pidió que dejáramos...

This is very common:

• Me pidió que fuera. = She asked me to go.
• Nos pidió que esperáramos. = She asked us to wait.

If the subject stays the same, Spanish usually prefers the infinitive instead:

• Pidió salir = He/she asked to leave.

But in your sentence, the teacher asked us, not herself, so the subjunctive is needed.

Because after pidió que, Spanish needs a finite verb in the subjunctive, not an infinitive.

So:

• La profesora nos pidió que escribiéramos...
• not La profesora nos pidió que escribir...

The infinitive escribir or dejar would only work in a different structure, usually when there is no change of subject:

• La profesora quiso escribir...
• La profesora decidió dejar...

In your sentence, the teacher is asking us to perform the actions, so Spanish uses the imperfect subjunctive forms escribiéramos and dejáramos.

Because the main verb is in the past: pidió.

When the main verb is in a past tense and it triggers the subjunctive, Spanish often uses the imperfect subjunctive in the subordinate clause:

• Nos pidió que escribiéramos...
• Nos pidió que dejáramos...

This is part of the normal sequence of tenses in Spanish.

Compare:

• Present: Nos pide que escribamos.
• Past: Nos pidió que escribiéramos.

So escribiéramos and dejáramos match the past context created by pidió.

Nos means us.

In this sentence, it is the indirect object of pidió:

• La profesora nos pidió... = The teacher asked us...

It tells you who received the request.

Other examples:

• Me pidió... = She asked me...
• Te pidió... = She asked you...
• Les pidió... = She asked them / you all...

So nos is not the subject. The subject is la profesora.

Because both verbs belong to the same request and share the same structure after pidió que.

So Spanish can say:

• La profesora nos pidió que escribiéramos el título... y dejáramos margen...

The second verb is coordinated with the first one, so repeating que is unnecessary.

You could repeat it for emphasis or clarity in some contexts, but it is not needed here:

• ...pidió que escribiéramos... y que dejáramos...

Both are possible, but the version with one que is perfectly natural and very common.

Because the teacher asked us, and us corresponds to nosotros / nosotras.

So the verbs must match that subject:

• escribiéramos = we wrote / we should write
• dejáramos = we left / we should leave

These are the imperfect subjunctive, nosotros forms of:

• escribir
• dejar

If the teacher were speaking to one student, you might get:

• La profesora le pidió que escribiera... y dejara...

If she were speaking to all of you directly in a different kind of sentence, you might also see other forms depending on the context.

Hoja literally means sheet or leaf, and in school or writing contexts it often means a physical sheet of paper.

So:

• en la primera hoja = on the first sheet/page

Spanish can also use página, but that usually refers more clearly to a numbered page in a book, notebook, or document.

Very roughly:

• hoja = sheet of paper
• página = page

In a classroom instruction about written work, hoja sounds very natural.

Because escribir en is the normal way to say write on/in a page, sheet, notebook, etc.

So Spanish commonly says:

• escribir en una hoja
• escribir en la pizarra
• escribir en el cuaderno

Using sobre is possible in some contexts, but it is less neutral here. En la primera hoja is the standard classroom phrasing.

Here dejar means to leave, and margen means margin.

So dejar margen means to leave a margin.

Then a la izquierda tells you where:

• a la izquierda = on the left / on the left-hand side

So the structure is basically:

• dejar
  • margen
    • a la izquierda

This is a normal classroom or handwriting instruction in Spanish.

Because Spanish normally uses a la izquierda and a la derecha to mean on the left and on the right.

These are fixed, very common expressions:

• Está a la izquierda.
• Escribe tu nombre a la derecha.
• Deja margen a la izquierda.

Using en la izquierda is generally not the normal choice for this idea.

Because in Spanish, instructions often omit the indefinite article when talking about a general amount or type of thing.

So dejar margen sounds natural as a general instruction: leave margin space.

You may also hear:

• dejar un margen
• dejar margen

Both can be possible, but dejar margen is very common in classroom instructions and sounds slightly more general and idiomatic here.

Yes, but the nuance changes a little.

In Spain:

• profesora is a very standard word for a female teacher, especially in secondary school and beyond.
• maestra is more strongly associated with primary school, though usage can vary.

So la profesora is a very natural choice here, especially in a general educational context.

Pidió is the pretérito indefinido form of pedir, third person singular:

• yo pedí
• tú pediste
• él/ella pidió
• nosotros pedimos
• vosotros pedisteis
• ellos pidieron

Here it means asked:

• La profesora nos pidió... = The teacher asked us...

It refers to a completed action in the past.