Moj običaj je da ujutro najprije pijem vodu, a tek onda kavu.

Literally, Moj običaj je means My habit/custom is.

In this sentence, običaj is being used in the sense of a habit or usual practice. So the whole start means something like:

• My habit is...
• What I usually do is...

It is understandable and correct, but it can sound a little more formal or descriptive than the most everyday way of saying it.

Very common alternatives are:

• Moja navika je da... = My habit is to...
• Imam običaj... = I have a habit of... / I usually...
• Običaj mi je da... = It is my habit to...

So yes, it is natural, but not the only way to express the idea.

Because običaj is a masculine noun in Croatian.

The possessive adjective has to agree with the noun it describes:

• moj običaj — masculine
• moja navika — feminine
• moje... — neuter

So:

• moj običaj = my habit/custom
• moja navika = my habit

This is basic adjective agreement in Croatian: possessives behave like adjectives and match the noun in gender, number, and case.

Croatian often uses da + present tense where English might use an infinitive.

So instead of saying something exactly like My habit is to drink..., Croatian naturally says:

• Moj običaj je da...
• literally: My habit is that I...

That sounds unusual in English, but it is normal in Croatian.

So:

• je da pijem = is that I drink / is to drink

Croatian does have infinitives, but after expressions like this, da + present is extremely common and natural.

Because in Croatian, the present tense is commonly used to express habitual actions, just like in English.

Compare:

• I drink water first in the morning — English present tense for habit
• Ujutro najprije pijem vodu — Croatian present tense for habit

So pijem here does not mean only I am drinking right now. In this context, it means I drink / I usually drink.

The sentence is describing a routine, so the present tense is the normal choice.

Ujutro means in the morning.

It is an adverbial expression, so you do not need a preposition like in before it. Croatian simply says:

• ujutro = in the morning

Examples:

• Ujutro pijem kavu. = I drink coffee in the morning.
• Ujutro učim. = I study in the morning.

So in your sentence:

• da ujutro najprije pijem vodu = that in the morning I first drink water

Both najprije and prvo can mean first.

In this sentence, najprije means first / first of all / before anything else.

You could often replace it with prvo:

• Ujutro najprije pijem vodu...
• Ujutro prvo pijem vodu...

Both are natural.

A rough difference:

• prvo is very common and straightforward
• najprije can sound a bit more careful or slightly more formal/stylistic

There is also regional variation, and in everyday speech many people use prvo very often.

A tek onda means something like:

• and only then
• and only after that
• and not until then

This adds a contrast: the speaker does not drink coffee immediately. First water, only then coffee.

Breakdown:

• a = and / while / but depending on context; here it introduces a contrast
• tek = only / not until
• onda = then

So:

• najprije pijem vodu, a tek onda kavu = I first drink water, and only then coffee

This is stronger than just and then. It emphasizes the order.

Because a often links two parts of a sentence with a sense of contrast or switching focus.

Here the pattern is:

• first water
• and only then coffee

So a works well because it sets up the second stage in contrast to the first.

Compare:

• i = simple and
• a = and / whereas / while / and then on the other hand

In this sentence, a sounds more natural than i, because the speaker is contrasting the two steps of the routine.

Because they are direct objects of the verb pijem (I drink), so they go into the accusative case.

Base forms:

• voda = water
• kava = coffee

Accusative singular:

• vodu
• kavu

So:

• pijem vodu = I drink water
• pijem kavu = I drink coffee

This is a very common pattern with feminine nouns ending in -a:

• nominative: voda

• accusative: vodu

• nominative: kava
• accusative: kavu

Because Croatian, like English, often omits a repeated verb when it is already clear from context.

So:

• najprije pijem vodu, a tek onda kavu

really means:

• najprije pijem vodu, a tek onda pijem kavu

The second pijem is simply left out because it would be repetitive and unnecessary.

English does the same thing:

• I drink water first, and only then coffee

instead of

• I drink water first, and only then I drink coffee

So the omission is completely normal.

Yes. Croatian word order is fairly flexible, although some versions sound more natural in certain contexts.

The given sentence is very natural:

• Moj običaj je da ujutro najprije pijem vodu, a tek onda kavu.

But you might also hear variations like:

• Moj običaj je da najprije ujutro pijem vodu, a tek onda kavu.
• Ujutro najprije pijem vodu, a tek onda kavu.
  (without Moj običaj je da, just stating the routine directly)
• Običaj mi je da ujutro najprije pijem vodu, a tek onda kavu.

The original order is good because it flows clearly:

1. topic: my habit is
2. time: in the morning
3. sequence: first
4. action: I drink water
5. contrastive follow-up: and only then coffee

Often, yes.

Both can work, but they are not always exactly the same in feel:

• navika = habit
• običaj = custom / usual practice / habit

In a sentence about a personal daily routine, many learners will hear navika more often:

• Moja navika je da ujutro najprije pijem vodu, a tek onda kavu.

That may sound slightly more like a personal habit.

Meanwhile, običaj can also refer to broader customs or established practices, not just personal habits.

Still, in this sentence, moj običaj is perfectly understandable and acceptable.

Yes. A very common simpler version would be:

• Ujutro najprije pijem vodu, a tek onda kavu.

This already clearly means:

• In the morning I first drink water, and only then coffee.

If the meaning has already been shown to the learner, this is probably the most direct everyday way to express the idea.

Other natural alternatives include:

• Imam običaj ujutro najprije piti vodu, a tek onda kavu.
• Obično ujutro najprije pijem vodu, a tek onda kavu.

So the original sentence is correct, but it is a bit more explicit than everyday speech needs to be.