Krećemo rano.

Because the verb form already tells you the subject.

In krećemo, the ending -mo means we. Serbian often leaves out subject pronouns when they are obvious from the verb.

So:

• krećem = I set off / I am leaving
• krećeš = you set off / you are leaving
• krećemo = we set off / we are leaving

You can still add mi for emphasis or contrast:

• Mi krećemo rano, a oni kasnije.
  We are leaving early, and they are leaving later.

The form krećemo is the 1st person plural present tense form of kretati or, in many contexts, the verb pair kretati / krenuti.

A useful way to think about it is:

• kretati = imperfective, ongoing/repeated/general
• krenuti = perfective, to start off / set off once

In everyday speech, krećemo is very natural for we are leaving / setting off.

Formally, it is present tense.

But in Serbian, present-tense forms can often be used for a planned or arranged future, especially with imperfective verbs and when the context is clear.

So Krećemo rano is grammatically present, but it can mean something like:

• We are leaving early
• We leave early

This is similar to English sentences like:

• We leave tomorrow at six.
• We are leaving early.

That is a very good question.

kretati se often means to move, to be moving, or to move around in a more general sense.

But kretati without se is also common when it means to set off, to depart, or to start going somewhere.

So:

• Krećemo rano. = We are setting off / leaving early.
• Brzo se krećemo. = We are moving quickly.

In this sentence, the meaning is about departure, so leaving out se is normal.

Here rano is an adverb, and it means early.

It modifies the verb krećemo, telling you when the action happens.

So the structure is:

• krećemo = we are leaving / setting off
• rano = early

As an adverb, rano does not change for gender, number, or case.

No. Rano is an adverb here, so it does not have case.

Cases apply to nouns, pronouns, adjectives, and some numbers, but not to adverbs used like this.

So in Krećemo rano, you do not need to analyze rano by case. It is simply the adverb early.

Yes, you can.

Both are correct, but the emphasis changes a little:

• Krećemo rano. = neutral statement
• Rano krećemo. = extra focus on early

Serbian word order is more flexible than English word order, because endings often carry the grammatical information. Even so, different orders can sound more or less natural depending on emphasis and context.

They are close, but not identical.

• krećemo focuses on setting off / starting the trip / departing
• idemo is broader and usually means we go / we are going

So:

• Krećemo rano suggests we start out early
• Idemo rano can also mean we go early, but it does not focus as strongly on the moment of departure

In many situations, both may be possible, but krećemo often sounds more natural when talking about leaving on a trip or starting a journey.

Yes, absolutely.

Mi krećemo rano is correct, but mi is usually added only when you want emphasis, contrast, or clarity.

Compare:

• Krećemo rano. = neutral
• Mi krećemo rano. = we are leaving early

For example:

• Mi krećemo rano, a vi ostajete duže.
  We are leaving early, and you are staying longer.

So the pronoun is optional, not wrong.

A rough English-friendly approximation is KRE-che-mo, but that is only approximate.

The important sound for many learners is ć:

• ć is a soft sound
• it is somewhat like a very soft ch
• it is softer than č

So krećemo is not pronounced with a hard English kret-semo or kretchemo. The middle sound is softer.

If you are just starting, aiming for something close to KRE-che-mo is a reasonable first step.