Με λίγη επανάληψη κάθε μέρα, πετυχαίνω καλύτερο αποτέλεσμα.

It is built into the verb πετυχαίνω.

In Greek, subject pronouns are often omitted because the verb ending already shows the person and number.
πετυχαίνω means I achieve / I get / I obtain.

So Greek does not need a separate εγώ (I) here.
If you added εγώ, it would usually sound more emphatic: I achieve a better result.

Με here means with.

It introduces the phrase με λίγη επανάληψη = with a little repetition.

In Greek, με is followed by the accusative case, so the noun phrase after it is in the accusative.

Because λίγη has to agree with επανάληψη.

• επανάληψη = a feminine noun
• λίγη = feminine singular form of λίγος (little / a little / some)

So the adjective must match the noun in gender, number, and case.

That is why you get:

• λίγη επανάληψη = a little repetition

Not λίγο επανάληψη, because λίγο is neuter.

It is in the accusative singular, because it follows με.

A useful thing to notice is that for many feminine nouns like επανάληψη, the nominative and accusative singular look the same. So even though the form is still επανάληψη, its role in the sentence is accusative.

Greek often leaves out the indefinite article (a/an) when English would use one.

So:

• με λίγη επανάληψη = with a little repetition
• καλύτερο αποτέλεσμα = a better result

This is very natural in Greek.

You could sometimes add ένα before καλύτερο αποτέλεσμα, but here it is not necessary. Without the article, the sentence sounds smooth and general.

κάθε μέρα means every day.

• κάθε = each / every
• μέρα = day

This is a very common time expression in Greek. It functions adverbially, telling you how often the action happens.

So the sentence is describing a habit or repeated action: with a little repetition every day, I get a better result.

Here πετυχαίνω means I achieve, I obtain, or I get.

The verb can have a few related meanings in Greek, depending on context, such as:

• to succeed
• to achieve
• to hit
• sometimes even to happen to find/meet

In this sentence, the meaning is clearly to achieve/get:
πετυχαίνω καλύτερο αποτέλεσμα = I achieve / get a better result.

The present tense in Greek is often used for habitual or general statements, just like in English.

So πετυχαίνω here does not just mean something happening right this second. It means something like:

• I get a better result
• I achieve a better result
• I tend to get a better result

Because of κάθε μέρα (every day), the sentence clearly describes a repeated pattern.

Because καλύτερο must agree with αποτέλεσμα.

• αποτέλεσμα is neuter singular
• καλύτερο is the neuter singular form of better

So:

• καλύτερο αποτέλεσμα = better result

This is the comparative form of καλός (good), so καλύτερος / καλύτερη / καλύτερο means better.

Greek word order is fairly flexible.

The sentence starts with Με λίγη επανάληψη κάθε μέρα to highlight the condition or method first: With a little repetition every day...

But other orders are also possible, for example:

• Πετυχαίνω καλύτερο αποτέλεσμα με λίγη επανάληψη κάθε μέρα.

That still means essentially the same thing.

The version you were given sounds natural and slightly emphasizes the idea of with a little repetition every day before giving the result.

The comma separates the introductory phrase from the main clause.

• Με λίγη επανάληψη κάθε μέρα = introductory adverbial phrase
• πετυχαίνω καλύτερο αποτέλεσμα = main clause

This punctuation helps readability. In English, we often do the same thing:

• With a little repetition every day, I get a better result.

So the comma is not changing the meaning; it is just organizing the sentence clearly.