Što pažljivije čitaš, to bolje razumeš.

It’s the Serbian equivalent of the English correlative comparative pattern the more ..., the more ... or the more ..., the better ....

So:

• Što pažljivije čitaš, to bolje razumeš.
• literally: The more carefully you read, the better you understand.

In this pattern:

• što introduces the first comparison
• to introduces the result in the second part

This is a very common structure in Serbian.

More examples:

• Što više vežbaš, to si bolji.
  The more you practice, the better you are.

• Što brže ideš, to pre stižeš.
  The faster you go, the sooner you arrive.

No. In this sentence, što does not mean what.

Here, što is part of the fixed comparative pattern što ..., to ..., meaning:

• the more ...
• the less ...
• the better ..., depending on context

So in this sentence, don’t interpret što on its own as a question word.

Not really. In this structure, to is not functioning like ordinary that.

It is the second half of the pair što ..., to ..., and together they express a linked comparison:

• Što X, to Y
• The more X, the more Y

So to here is best understood as part of the grammatical pattern, not as a separately translated word.

They are comparative adverbs.

1. pažljivo → pažljivije

• pažljivo = carefully
• pažljivije = more carefully

2. dobro → bolje

• dobro = well
• bolje = better

In the sentence:

• čitaš is a verb, so it needs an adverb: pažljivije = more carefully
• razumeš is also a verb, so bolje means better

This is why you do not use adjective forms here.

Because pažljivije is an adverb, while pažljiviji is an adjective.

Compare:

• pažljiv čovek = a careful man
  adjective

• pažljivo čita = he/she reads carefully
  adverb

In your sentence, the word describes how someone reads, so Serbian uses the adverb:

• pažljivije čitaš = you read more carefully

Not:

• pažljiviji čitaš ❌

Razumeš is the 2nd person singular present tense of razumeti / razumjeti, meaning to understand.

So:

• ja razumem = I understand
• ti razumeš = you understand
• on/ona razume = he/she understands

In this sentence, the subject is an understood you, so:

• čitaš = you read
• razumeš = you understand

Serbian often leaves the subject pronoun out because the verb ending already shows the person.

Because Serbian usually omits subject pronouns when they are clear from the verb ending.

Here:

• čitaš already means you read
• razumeš already means you understand

So the full version with the pronoun would be:

• Što pažljivije ti čitaš, to bolje ti razumeš.

But that sounds unnecessary in normal speech unless you want emphasis or contrast. The natural version is:

• Što pažljivije čitaš, to bolje razumeš.

Because Serbian uses the present tense here to express a general truth or regular relationship, just like English often does:

• The more carefully you read, the better you understand.

This is not about one specific moment only. It expresses a general principle.

Serbian commonly uses present tense for this kind of statement.

No, that would not be standard here.

In this comparative construction, the normal word is što, not šta.

So use:

• Što pažljivije čitaš, to bolje razumeš. ✅

Not:

• Šta pažljivije čitaš, to bolje razumeš. ❌

Yes. The sentence is understandable and acceptable, but it reflects a mix of features that may remind learners of different regional standards.

• što in this construction is normal
• razumeš is typical of Ekavian Serbian
• In Ijekavian varieties, you may also see razumiješ

So you may encounter:

• Što pažljivije čitaš, to bolje razumeš.
• Što pažljivije čitaš, to bolje razumiješ.

Both mean the same thing; the difference is regional/standard variation.

No, not in the same way.

This sentence is not a normal if-clause. It is a correlative comparative structure.

So:

• Što pažljivije čitaš, to bolje razumeš.
  The more carefully you read, the better you understand.

If you use ako, the meaning shifts more toward a condition:

• Ako pažljivije čitaš, bolje razumeš.
  If you read more carefully, you understand better.

That is possible, but it is not quite the same pattern or nuance.

Yes, but the basic paired structure should stay recognizable:

• Što pažljivije čitaš, to bolje razumeš.
  standard and natural

You may sometimes hear slight variations for emphasis, but this version is the safest and most natural for learners.

The important thing is to keep:

• što + comparative
• to + comparative

It works with both more and less, depending on the comparative word you use.

Examples:

• Što više čitaš, to više znaš.
  The more you read, the more you know.

• Što manje spavaš, to si umorniji.
  The less you sleep, the more tired you are.

• Što sporije voziš, to si bezbedniji.
  The more slowly you drive, the safer you are.

So the construction is flexible.

A helpful word-for-word breakdown is:

• Što = part of the more ...
• pažljivije = more carefully
• čitaš = you read
• to = part of the ..., the ... pattern
• bolje = better
• razumeš = you understand

So a very literal gloss would be:

• The more carefully you read, the better you understand.

That is also the best natural translation into English.