Ako si sama u centru, gledaj mapu i pozovi me.

Sama means alone and it agrees with the person being spoken to.

Because the sentence is addressed to one female person, Serbian uses the feminine singular form:

• masculine: sam
• feminine: sama

So:

• Ako si sam u centru... = if you are alone in the center (to a man)
• Ako si sama u centru... = if you are alone in the center (to a woman)

This is something English does not show, because you are alone stays the same regardless of gender.

Serbian often leaves out subject pronouns when they are already clear from the verb form.

Here, the forms already show who is being addressed:

• si = you are
• gledaj = look
• pozovi = call

So ti is not necessary.
You could say Ako si ti sama u centru..., but that would add emphasis, something like if you yourself are alone downtown...

Because u can take different cases depending on meaning:

• u + locative = location, in / at
• u + accusative = movement into, into

Here the meaning is location: you are in the center, not moving into it.

So:

• u centru = in the center / downtown
• u centar = into the center

Also, centru is the locative singular form of centar.

It can mean both, depending on context.

In everyday speech, u centru very often means:

• in the city center
• downtown

But literally it is simply in the center.
Without more context, a learner should understand it as in the center / downtown.

Because mapu is the accusative singular form, and it is the direct object of gledaj.

• nominative: mapa = a map
• accusative: mapu = the map / a map as an object

Serbian usually changes noun endings depending on grammatical function.
Here, the command is look at the map, so mapa becomes mapu.

That is a very common difference between English and Serbian.

With gledati, Serbian often uses a direct object where English uses look at:

• gledaj mapu = look at the map
• gledam televiziju = I’m watching TV
• gledao je nebo = he looked at the sky

So you do not need a separate word meaning at here.

There is also gledati u + accusative, but that often has a slightly different feel, more like look into / stare at something.

They are imperative forms, used for commands or instructions.

Here they are 2nd person singular, so they are used when speaking to one person informally.

• gledaj = look
• pozovi = call

If you were speaking politely or to more than one person, you would use:

• gledajte
• pozovite

This is about aspect, which is very important in Serbian.

• gledaj comes from gledati (imperfective)
• pozovi comes from pozvati (perfective)

Why this combination?

• gledaj mapu suggests the action as a process: look at / use the map
• pozovi me suggests one complete action: give me a call

If you said zovi me, from zvati (imperfective), it could sound more like:

• call me repeatedly
• keep calling me
• call me in general

So pozovi me is the natural choice for call me once.

Me is the short, unstressed form of I / me in the accusative.

• me = short form
• mene = full, stressed form

In a neutral sentence, Serbian prefers the short form:

• pozovi me = call me

You would use mene for emphasis or contrast:

• Pozovi mene, ne njega. = Call me, not him.

Because short pronoun forms like me, mi, ga, je, ih have special placement rules in Serbian.

After an imperative, they normally come right after the verb:

• Reci mi. = Tell me.
• Daj mi mapu. = Give me the map.
• Pozovi me. = Call me.

So pozovi me is the normal word order.

Yes, it could.

Both are possible, but the nuance is a little different:

• Ako si sama u centru... = if you are / if you happen to be alone downtown
• Ako budeš sama u centru... = if you end up being / if you will be alone downtown

The version with si is very natural in everyday instructions.
The version with budeš makes the future situation a bit more explicit.

So the sentence you have is perfectly normal, especially as practical advice.

It is informal, because it uses 2nd person singular imperative:

• gledaj
• pozovi

This is the form you use with:

• one friend
• a family member
• someone you address with ti

A formal or plural version would be:

• Ako ste sami u centru, gledajte mapu i pozovite me.

That can mean either:

• speaking politely to one person, or
• speaking to several people