Es importante que nos esforcemos más si queremos mejorar.

Because Es importante que... normally triggers the subjunctive in Spanish.

Here, Es importante expresses a judgment or necessity, so the verb in the que-clause goes into the present subjunctive:

• Es importante que nos esforcemos más
• not Es importante que nos esforzamos más

So esforcemos is the correct present subjunctive form for nosotros.

It comes from the verb esforzarse, which means to make an effort or to try hard.

• esforzarse = infinitive
• nos = reflexive pronoun meaning ourselves
• esforcemos = we make an effort / we try hard in the subjunctive

So nos esforcemos literally means something like that we make an effort.

The nos is part of the verb because esforzarse is a reflexive verb.

In Spanish, reflexive pronouns usually go before a conjugated verb.

So you get:

• nos esforcemos

But with an infinitive, gerund, or affirmative command, the pronoun is often attached to the end:

• esforzarnos
• esforzándonos

Since esforcemos is a conjugated verb, nos has to come before it.

This is a very common learner question because esforzarse has both a stem change and a spelling change.

1. Stem change

In the present indicative, the verb changes o → ue in stressed forms:

• yo esfuerzo
• tú esfuerzas
• él/ella esfuerza
• nosotros nos esforzamos
• vosotros os esforzáis
• ellos esfuerzan

In the present subjunctive, the nosotros and vosotros forms usually go back to the original stem:

• yo me esfuerce
• tú te esfuerces
• él/ella se esfuerce
• nosotros nos esforcemos
• vosotros os esforcéis
• ellos se esfuercen

So that is why it is esforcemos, not esfuercemos.

2. Spelling change

The infinitive has z: esforzar.
Before e, Spanish usually changes z to c in these verb forms:

• esforcemos
• esforcéis

So esforzemos is not the standard form.

Because si meaning if normally takes the indicative when you are talking about a real or possible condition.

So:

• si queremos mejorar = if we want to improve

This is a normal, open condition, so queremos is in the present indicative.

Spanish does not usually use the present subjunctive after si in this kind of sentence.

Compare:

• Si queremos mejorar, ... = real possibility
• Si quisiéramos mejorar, ... = if we wanted to improve, more hypothetical

Because after querer, Spanish uses an infinitive when the subject of both verbs is the same.

Here, the same people are doing both actions:

• queremos = we want
• mejorar = to improve

So queremos mejorar means we want to improve.

If the subject changed, Spanish would use que + subjunctive instead:

• Queremos que ellos mejoren = We want them to improve

Here que introduces a subordinate clause, very much like that in English.

Structure:

• Es importante que + subjunctive

So:

• Es importante que nos esforcemos más

Literally, this is It is important that we make more effort.

In English, that is often omitted, but in Spanish que is required here.

Here más means more, and it modifies nos esforcemos.

So the idea is:

• esforzarnos más = to make more effort
• try harder

Its position after the verb is very natural in Spanish. You will often see más after the verb when it modifies the action:

• trabajar más
• estudiar más
• esforzarse más

So nos esforcemos más is the normal word order.

Yes. That version is completely natural.

Both are correct:

• Es importante que nos esforcemos más si queremos mejorar
• Si queremos mejorar, es importante que nos esforcemos más

The difference is mainly emphasis:

• starting with Es importante... emphasizes the importance
• starting with Si queremos mejorar... emphasizes the condition first

Yes, that is also correct.

Compare:

• Es importante que nos esforcemos más
• Es importante esforzarnos más

Both are natural and mean almost the same thing.

Slight difference

• Es importante que nos esforcemos más sounds a bit more like a full clause with emphasis on we should make the effort
• Es importante esforzarnos más is a little more compact and direct

Spanish often allows both patterns:

• Es bueno que estudiemos
• Es bueno estudiar

Because Es importante is an impersonal expression.

It works like English It is important. The it in English does not refer to a real thing, and Spanish often just uses es with an adjective:

• Es importante
• Es necesario
• Es posible
• Es mejor

So there is no specific subject here. It is just a general statement.

Not in the usual sense of a direct object like us in They saw us.

Here, nos is a reflexive pronoun, part of the verb esforzarse. It shows that the action refers back to the subject:

• nos esforcemos = we make an effort ourselves

So it is better to think of nos esforzarse as one unit when learning the verb:

• esforzarse = to make an effort
• me esfuerzo
• te esfuerzas
• se esfuerza
• nos esforzamos

That will help it feel more natural.