Na obrascu trebaš pisati što urednije.

Na obrascu means on the form.

Croatian often uses na with things like forms, lists, documents, and surfaces where something is written or appears. So you write na obrascu, just as you also get expressions like na papiru (on paper).

Here, obrascu is the locative singular of obrazac (form), because na can take the locative when it means location.

So:

• obrazac = form
• na obrascu = on the form

Using u obrascu would usually not sound natural here, because the idea is not really inside the form in a physical sense, but on it / on the document.

Trebaš means you need to / you should here.

It comes from the verb trebati, which is often used to express necessity, obligation, or advice.

So:

• trebaš pisati = you should write / you need to write

This structure is very common:

• trebam učiti = I need to study
• trebaš doći = you should come
• treba raditi = one should work / it is necessary to work

In this sentence, trebaš is 2nd person singular, so it is speaking directly to one person: you.

Pisati is the infinitive, because it follows trebaš.

After trebati, Croatian normally uses an infinitive:

• trebaš pisati
• trebaš čekati
• trebaš doći

If the sentence used piši, that would be an imperative:

• Piši urednije. = Write more neatly.

So the difference is roughly:

• Trebaš pisati... = You should write...
• Piši... = Write... (direct command)

Also, pisati is the imperfective verb, which fits well here because the sentence is about the general manner of writing, not one completed act.

Here što means something like as ... as possible.

So što urednije means:

• as neatly as possible
• literally something like the more neatly possible

This is a very common Croatian pattern:

• što brže = as quickly as possible
• što bolje = as well as possible
• što prije = as soon as possible
• što jasnije = as clearly as possible

So in your sentence:

• urednije = more neatly
• što urednije = as neatly as possible

This što is not the same as the relative/interrogative what.

Because the sentence is expressing a comparison/intensification: not just neatly, but more neatly / as neatly as possible.

The base adverb is:

• uredno = neatly, tidily

The comparative adverb is:

• urednije = more neatly

And then:

• što urednije = as neatly as possible

So the sentence is not merely saying write neatly, but write as neatly as possible.

It comes from the adjective uredan (neat, tidy).

Croatian often forms adverbs from adjectives, and then comparatives from those adverbs.

A simplified path is:

• uredan = neat, tidy
• uredno = neatly
• urednije = more neatly

So in this sentence, urednije is an adverb in the comparative, describing how you should write.

It modifies the verb pisati.

Obrascu is in the locative singular.

The dictionary form is:

• obrazac = form

After the preposition na, when it means on / at a location, Croatian uses the locative:

• na obrascu = on the form

So:

• nominative: obrazac
• locative singular: obrascu

This change is normal for masculine nouns in this pattern.

It depends on context.

Trebaš can mean:

• you should
• you need to
• sometimes almost you must

In a sentence like Na obrascu trebaš pisati što urednije, it usually sounds like an instruction or recommendation, so English should is often the best choice.

If Croatian wanted a clearly stronger sense of obligation, it might use:

• moraš = you must

Compare:

• trebaš pisati što urednije = you should / need to write as neatly as possible
• moraš pisati što urednije = you must write as neatly as possible

Yes. Croatian word order is more flexible than English word order.

The given sentence:

• Na obrascu trebaš pisati što urednije.

is natural and clear.

But you could also hear things like:

• Trebaš na obrascu pisati što urednije.
• Što urednije trebaš pisati na obrascu.

These versions may shift emphasis slightly, but the basic meaning stays the same.

The original version sounds like a normal instruction, with na obrascu placed first to set the context: on the form.

Yes, but it is built into the verb.

Croatian often leaves subject pronouns unstated because the verb ending already shows the person.

Here:

• trebaš = you should / you need to

The ending -š tells you it is 2nd person singular.

So the sentence does not need ti.

You could say:

• Ti trebaš pisati što urednije.

but that would usually add emphasis, contrast, or stress. In normal speech, trebaš by itself is enough.