Trebalo bi da sediš ovde i da popuniš ovaj obrazac pre nego što dođeš na šalter.

Trebalo bi da... usually means you should... / you ought to....

So:

Trebalo bi da sediš ovde i da popuniš ovaj obrazac...
= You should sit here and fill out this form...

It sounds like a recommendation or polite instruction. It is generally softer than moraš da... (you must / have to...).

In this pattern, trebalo bi da + present tense is a very common impersonal construction in Serbian.

The trebalo here does not agree with the person being spoken to. It functions as a fixed, neutral form meaning something like it would be advisable / one should.

That is why you get:

• Trebalo bi da sediš = You should sit
• Trebalo bi da sedim = I should sit
• Trebalo bi da sedimo = We should sit

Only the verb after da changes for person.

Bi is the conditional particle. It softens the expression and gives it the sense of should / would be good to.

Compare:

• Treba da popuniš obrazac. = You need to / should fill out the form.
  Often stronger, more direct.
• Trebalo bi da popuniš obrazac. = You should fill out the form.
  More polite, less forceful.

So bi helps make the statement sound less like a command and more like advice or polite instruction.

Because Serbian very often uses da + present tense where English uses an infinitive.

So English:

• You should sit
• You should fill out

becomes Serbian:

• trebalo bi da sediš
• trebalo bi da popuniš

This is one of the most important patterns in Serbian. After many verbs and expressions, especially modal-like ones, da + present is preferred or standard.

This is mainly about aspect.

• sediš comes from sedeti (to be sitting / to sit in an ongoing sense) — imperfective
• popuniš comes from popuniti (to fill out completely) — perfective

Why this difference?

• sediš ovde describes an ongoing state: sit here / be seated here
• popuniš ovaj obrazac focuses on completing the action: fill out this form

So the sentence naturally combines:

• an ongoing activity/state (sediš)
• a completed action (popuniš)

Yes, but it would change the meaning.

• sediš = sit / be sitting
• sedneš = sit down

So:

• Trebalo bi da sediš ovde... = You should sit here / be seated here...
• Trebalo bi da sedneš ovde... = You should sit down here...

The original sentence suggests remaining seated while filling out the form, not just the one-time action of taking a seat.

Because Serbian often repeats da before each coordinated verb clause, especially in careful or standard phrasing.

So:

• da sediš ovde i da popuniš ovaj obrazac

is completely normal and very natural.

You may also hear the second da omitted in casual speech:

• da sediš ovde i popuniš ovaj obrazac

But repeating it is clearer and very common.

Pre nego što means before.

So:

pre nego što dođeš na šalter
= before you come to the counter

It introduces a subordinate clause. After it, Serbian uses a finite verb, not an infinitive.

A useful way to think of it:

• pre nego što + verb = before + subject + verb

Examples:

• pre nego što odeš = before you leave
• pre nego što počneš = before you begin

Again, this is about aspect.

• dođeš is from doći — perfective
• dolaziš is from dolaziti — imperfective

Here the sentence refers to one completed arrival at the counter, so dođeš fits better:

• pre nego što dođeš na šalter = before you come / arrive at the counter

If you used dolaziš, it would sound more like repeated, habitual, or ongoing coming, which does not fit as well here.

Šalter is a service counter, window, or desk, especially in places like banks, post offices, government offices, and similar institutions.

So doći na šalter means to come up to the counter/window.

Serbian uses na with many service points:

• na šalter
• na kasu
• na pult

Here na šalter is in the accusative, because there is motion toward it:

• dođeš na šalter = you come to the counter

If you were talking about location, you would get the locative:

• na šalteru = at the counter

Ovaj obrazac is the direct object of popuniš, so it is in the accusative.

However, for many masculine inanimate nouns, the accusative looks the same as the nominative.

So:

• nominative: ovaj obrazac = this form
• accusative: ovaj obrazac = this form

That is why nothing visibly changes here.

Grammatically, trebalo bi da... often sounds like a recommendation: you should...

But in real-life contexts like offices, banks, hospitals, or government buildings, it can function as a polite instruction:

You should sit here and fill out this form before coming to the counter.

So the tone is softer than a direct command, but the practical meaning may still be: this is the proper procedure.