Eu escrevi o título, mas ainda preciso melhorar o primeiro parágrafo.

Yes. In Brazilian Portuguese, Eu is often optional because the verb form already shows who the subject is.

• Eu escrevi o título...
• Escrevi o título...

Both mean the same thing: I wrote the title...

Including Eu can add emphasis, contrast, or clarity. For example, if you want to stress I rather than someone else, using Eu sounds more natural.

Escrevi is the pretérito perfeito form of escrever, and it usually expresses a completed action in the past:

• Eu escrevi o título = I wrote the title

Here, the speaker sees writing the title as something finished.

By contrast:

• eu escrevia suggests an ongoing, repeated, or background past action
• tenho escrito means something more like I have been writing or I have written repeatedly lately, depending on context

So escrevi is the natural choice for one completed action.

Portuguese uses definite articles much more often than English.

So where English says:

• I wrote the title
• the first paragraph

Portuguese naturally says:

• o título
• o primeiro parágrafo

Even when English might leave the article out in some contexts, Portuguese often keeps it. In this sentence, o is completely normal and expected.

Mas means but, and ainda here means still.

So:

• mas ainda preciso melhorar... = but I still need to improve...

If you said only mas preciso melhorar..., it would mean but I need to improve..., which is also correct, but it loses the idea of still—that the work is not finished yet.

In Brazilian Portuguese, the most common structure is:

• precisar + infinitive

So:

• preciso melhorar = I need to improve

You may sometimes see precisar de before a noun:

• preciso de ajuda = I need help

With a verb, Brazilian Portuguese normally prefers precisar + infinitive without de.

It can mean both, depending on context.

In this sentence:

• preciso melhorar o primeiro parágrafo

the idea is I need to improve the first paragraph or I need to make the first paragraph better.

So melhorar can be:

• intransitive: something improves
• transitive: someone improves something

Here it is transitive, because the object is o primeiro parágrafo.

In Portuguese, ordinal numbers like primeiro, segundo, terceiro usually come before the noun:

• o primeiro parágrafo
• o segundo capítulo
• a terceira página

So o primeiro parágrafo is the standard word order.

Yes. Título can mean title, including the title of a text, article, essay, or section heading depending on context.

In this sentence, o título most naturally means the title of the piece of writing the speaker is working on.

Yes, very natural.

Eu escrevi o título, mas ainda preciso melhorar o primeiro parágrafo. sounds like something a Brazilian Portuguese speaker would really say when talking about writing.

A slightly shorter version, also very natural, would be:

• Escrevi o título, mas ainda preciso melhorar o primeiro parágrafo.

A few options are possible, but they can sound a little different:

• Escrevi o título...
  Simple and very natural: I wrote the title...

• Já escrevi o título...
  Adds the idea of already: I’ve already written the title...

• Tenho escrito...
  Usually suggests repeated or ongoing writing over a period of time, so it is less natural for a single completed result like the title

If your goal is the most natural everyday Brazilian Portuguese, Escrevi o título... or Já escrevi o título... is best.

No. In this sentence, preciso comes from the verb precisar, which means to need.

• eu preciso = I need

This is different from the adjective preciso, which can mean precise or accurate in other contexts:

• um valor preciso = a precise value

So in ainda preciso melhorar, preciso definitely means need.

It has two main parts joined by mas:

1. Eu escrevi o título

   • Eu = subject
   • escrevi = verb
   • o título = direct object

2. mas ainda preciso melhorar o primeiro parágrafo

   • mas = but
   • ainda = still
   • preciso = I need
   • melhorar = to improve
   • o primeiro parágrafo = direct object of melhorar

So the overall structure is:

• I wrote X, but I still need to improve Y