Because najlepiej is an adverb, while najlepszy is an adjective.
These are adjective forms, used to describe nouns.
But in this sentence, best describes how I work, so Polish uses the adverb:
So:
Not:
Pracuję is the 1st person singular present tense of pracować (to work).
So it means:
A few present-tense forms of pracować are:
The ending -ę is a very common marker for I in Polish verbs.
Because in Polish, the verb ending often already tells you who the subject is.
That is why Polish often drops subject pronouns unless they are needed for emphasis or contrast.
Compare:
So the version without ja is completely normal.
It can mean either, depending on context.
Polish present tense often covers both:
In this sentence, because of najlepiej and rano, it usually sounds like a general habit or tendency:
So the most natural interpretation is not I am working best right now, but rather mornings are when I function best for work.
Because rano can function on its own as an adverb of time.
So:
Polish does not need a preposition here.
Examples:
You can also say:
But rano is the most common everyday choice.
Yes. Polish word order is fairly flexible, although some versions sound more natural than others depending on emphasis.
The neutral version here is:
Other possible versions:
The basic meaning stays similar, but the focus shifts:
Yes, very often. That can confuse learners.
Najlepiej can mean:
best
best / preferably / the best thing would be
In your sentence, it clearly means best because it modifies the verb pracuję.
A rough pronunciation guide for an English speaker is:
A few useful pronunciation points:
They are very similar, but rano is more common in everyday speech.
Examples:
Both are correct, but rano is usually the more natural default in conversation.
rankiem can sound a little more literary or stylistically marked in some contexts.
You add nie before the verb:
But be careful: this sounds a little unusual if you mean the opposite of the original idea.
More natural alternatives might be:
Nie pracuję najlepiej rano, tylko wieczorem.
= I don’t work best in the morning, but in the evening.
Rano nie pracuję dobrze.
= I don’t work well in the morning.
So the best negative version depends on what exactly you want to deny:
Yes, but it is slightly different in tone.
So:
z rana is perfectly natural, but it is a bit more specific.