Ona marzy o awansie, ale wie, że najpierw musi lepiej planować swoją pracę.

Because the verb marzyć normally goes with the preposition o when it means to dream about or to dream of something.

So the pattern is:

• marzyć o + locative

Examples:

• marzyć o wakacjach = to dream about holidays
• marzyć o sukcesie = to dream of success
• marzyć o awansie = to dream of a promotion

Using marzy awans would be ungrammatical in standard Polish.

Because after o, this noun is in the locative case.

Base form:

• awans = promotion

Locative singular:

• o awansie = about a promotion / of a promotion

This is a very common thing in Polish: prepositions often require a specific case.

Here, the important pattern is:

• o + locative

So:

• o pracy = about work
• o domu = about the house
• o awansie = about a promotion

It means dreams of/about, not just wants.

There is a nuance:

• marzyć o = to dream of, to long for, to imagine having something
• chcieć = to want

So Ona marzy o awansie is a bit more emotional or aspirational than Ona chce awansu.

Compare:

• Ona chce awansu = She wants a promotion.
• Ona marzy o awansie = She dreams of a promotion.

Both are possible, but they are not identical in tone.

In Polish, a comma is normally placed before że when it introduces a subordinate clause.

So in:

• wie, że najpierw musi...

the part after że is a clause meaning that...

This is standard Polish punctuation:

• Myślę, że... = I think that...
• Wiem, że... = I know that...
• Mówi, że... = He/She says that...

Even when English might sometimes omit that, Polish still usually keeps że, and the comma stays.

Because after musi (must / has to), Polish often uses the infinitive.

So the structure is:

• musi + infinitive

Here:

• musi planować = must plan

Examples:

• musi pracować = must work
• musi iść = must go
• musi lepiej planować = must plan better

This is very similar to English:

• she must plan

Because planować is imperfective, and that fits better here.

Polish aspect matters a lot:

• planować = to plan, to be engaged in planning, to plan in a general or repeated way
• zaplanować = to plan out, to make a plan completely, often as a single completed action

In this sentence, the meaning is general:

• she needs to be better at planning her work
• not just make one plan once

So musi lepiej planować swoją pracę means she must improve her planning habit/ability.

If you said musi lepiej zaplanować swoją pracę, it would sound more like:

• she must plan her work better on a particular occasion or as a completed task

Because lepiej is the comparative form of dobrze:

• dobrze = well
• lepiej = better

So:

• dobrze planować = to plan well
• lepiej planować = to plan better

The sentence implies comparison:

• she already plans to some degree, but she needs to do it better

That is why lepiej is the natural choice.

Because Polish usually uses the reflexive possessive swój when the possessor is the subject of the sentence.

Here the subject is ona (she), and the work belongs to that same person. So Polish prefers:

• swoją pracę = her own work

This is more natural than jej pracę here.

A useful rule:

• use swój when the owner is the same as the subject

Examples:

• Ona lubi swoją pracę. = She likes her job.
• On myje swoje auto. = He washes his car.

By contrast, jej pracę usually suggests someone else’s work:

• Ona planuje jej pracę. = She is planning her work.
  Here jej would usually mean another woman’s, not her own.

It is in the accusative case because it is the direct object of planować.

Base forms:

• swoja / swoją comes from swój
• praca = work

In this sentence:

• planować co? = to plan what?
• swoją pracę = her work

For feminine nouns like praca, the accusative singular usually looks like this:

• praca → pracę

And the adjective/pronoun matches:

• swoja → swoją

So:

• swoją pracę is the correct accusative phrase.

Najpierw means first or first of all.

It shows sequence:

• she dreams of a promotion,
• but she knows that before that, she has to improve something.

So:

• najpierw musi lepiej planować swoją pracę means
• first she has to plan her work better

It connects the two ideas logically:

1. promotion is the goal
2. better planning is the necessary earlier step

Yes. Polish word order is fairly flexible, although some orders sound more natural than others depending on emphasis.

The given sentence is very natural:

• Ona marzy o awansie, ale wie, że najpierw musi lepiej planować swoją pracę.

But you could also say:

• Marzy o awansie, ale wie, że najpierw musi lepiej planować swoją pracę.

Since the verb ending already shows person, ona can often be omitted unless you want emphasis or contrast.

You could also move some words for emphasis, for example:

• Ona marzy o awansie, ale wie, że swoją pracę musi najpierw lepiej planować.

That is grammatical, but less neutral.

So the original version is a good standard model.

In this sentence, praca is best understood as work in the sense of her work/tasks, not necessarily her job position.

So:

• planować swoją pracę = plan her work / organize her work better

Depending on context, praca can mean:

• work
• job
• employment

But here, because of planować, it clearly means the work she does, her duties, her tasks, or how she organizes them.

Yes. Very often Polish drops subject pronouns when they are clear from the verb form.

So both of these are possible:

• Ona marzy o awansie...
• Marzy o awansie...

Why include ona then?

Usually for one of these reasons:

• emphasis
• contrast
• clarity in context

For example:

• Ona marzy o awansie, a on chce zmienić pracę. = She dreams of a promotion, and he wants to change jobs.

In an isolated example sentence, including ona is completely fine and often helpful for learners.