Learn Hardcore Croatian: Nakon posla spavanje mi je važno. - After work, sleeping is important to me.

Spavanje is a verbal noun (like English sleeping / sleep used as a thing). Croatian often uses verbal nouns where English might use an infinitive or -ing form.

spavati – to sleep (verb, infinitive)
spavanje – sleeping / sleep (noun)

In this sentence, spavanje is the subject of the verb je:

spavanje mi je važno – sleeping is important to me

You need a noun as the subject here, so spavanje is the natural choice.
Using spavati directly here (Nakon posla spavati mi je važno) is not standard; it sounds wrong/unnatural in Croatian.

What exactly does mi mean in spavanje mi je važno?

mi is the dative form of ja (I), and here it means to me / for me.

ja – I (nominative)
meni – to me (full dative form)
mi – to me (clitic dative form, short, unstressed)

So:

Spavanje mi je važno.
literally: Sleeping to-me is important.
natural English: Sleeping is important to me.

You could also say:

Spavanje je meni važno.

That version uses meni instead of mi and gives a bit more emphasis on to me (personally).

Why is the word order spavanje mi je važno, and not spavanje je mi važno?

In Croatian, short unstressed pronouns like mi are clitics and must follow quite strict word order rules.

Clitics like mi, ti, mu, joj, se, ga, je, sam, si, je, smo normally appear:

In the second position in the clause, and
In a specific internal order relative to each other.

In spavanje mi je važno:

Spavanje = first stressed word
mi = clitic in second position
je = another clitic following mi

So spavanje mi je važno is correct, while:

spavanje je mi važno sounds wrong because je has taken the clitic slot before mi, breaking the usual clitic ordering.

You’ll hear:

Spavanje mi je važno. (correct)
but not
Spavanje je mi važno. (incorrect/ungrammatical)

Why is važno with -o, not važan or važna?

The adjective važan (important) must agree in gender, number, and case with the noun it describes.

spavanje is a neuter noun (ends in -nje, and its gender is neuter)
So the adjective must be neuter singular nominative → važno

Forms:

masculine: važan
feminine: važna
neuter: važno

Since spavanje is the subject:

Spavanje mi je važno. (Sleeping is important to me.)

Other examples:

Učenje je važno. – Learning is important. (učenje = neuter)
Zdravlje je važno. – Health is important. (zdravlje = neuter)

Can I change the word order, like Spavanje mi je važno nakon posla or Važno mi je spavanje nakon posla?

Yes. Croatian word order is fairly flexible, and all of these are possible and correct, but they differ slightly in focus/emphasis:

Nakon posla spavanje mi je važno.
Neutral, light emphasis on after work as the time frame.
Spavanje mi je važno nakon posla.
Emphasis on spavanje first; then specify when it’s important.
Važno mi je spavanje nakon posla.
Emphasis on važno mi je (what is important to me), then clarify: it’s the sleep after work.
Nakon posla, važno mi je spavanje.
Similar meaning; comma can add a slight pause/emphasis.

All are understandable; which one you choose depends on what you want to highlight.

Could I say Nakon posla meni je važno spavanje instead of mi je?

Yes, but the nuance changes slightly.

mi je – unstressed, typical, neutral: is important to me
meni je – stressed, adds emphasis on me: to me (personally) it is important

So:

Nakon posla spavanje mi je važno.
neutral: Sleeping is important to me after work.
Nakon posla meni je važno spavanje.
implies contrast: For me, it’s sleep that’s important after work (maybe for others it’s something else).

Both are grammatically correct.

Can I drop mi and just say Nakon posla spavanje je važno?

Yes, but the meaning becomes more general and less personal.

Nakon posla spavanje mi je važno.
After work, sleep is important to me personally.
Nakon posla spavanje je važno.
After work, sleep is important. (in general; to people, to health, etc.)

So mi marks it specifically as your perspective.

Why not use a person + verb, like Moram spavati nakon posla, instead of this structure?

You can use sentences like:

Moram spavati nakon posla. – I have to sleep after work.
Želim spavati nakon posla. – I want to sleep after work.

But they express a slightly different meaning:

Spavanje mi je važno.
Describes a value/judgment: Sleep (as a thing) is important to me.
Moram spavati. / Trebam spavati.
Describes a necessity or obligation: I must / I need to sleep.

So the original sentence focuses on importance as a concept, not on a direct action you do.

How should I pronounce nakon posla spavanje mi je važno?

Approximate pronunciation (stressed syllables in bold):

NA-kon
PO-sla
SPA-va-nje
MI
je
VA-žno

Rough English approximations:

NÁ-kohn PÓ-slah SPÁH-vah-nyeh mee yeh VÁH-zhnoh

Key points:

nj in spavanje is a palatal sound like ñ in Spanish señor.
ž in važno is like s in English measure.
je is pronounced like ye in yes.
Final vowels are clearly pronounced; don’t drop them.