Learn Hardcore Russian: Пиши аккуратнее, чтобы не делать ошибок. - Write more neatly so as not to make mistakes.

Пиши is the imperative (command/request) form of писать (to write). It’s the 2nd person singular imperative, used when speaking informally to one person (you).

Is this sentence informal? How would it sound more polite?

Yes, пиши is informal (ты-form). A more polite/neutral version to one person would use вы:

Пишите аккуратнее, чтобы не делать ошибок.

You can also soften it further (more like advice than a command), e.g.:

Пишите, пожалуйста, аккуратнее…

Why is аккуратнее in the comparative form? Comparative of what?

Аккуратнее is the comparative of аккуратно (neatly / carefully). Comparative here means more carefully / more neatly—i.e., “write more carefully (than you are writing now).” Russian often uses the comparative like this to mean “be a bit more X.”

Could it be аккуратно instead of аккуратнее?

Yes, but the nuance changes:

Пиши аккуратно = “Write neatly/carefully.” (general instruction)
Пиши аккуратнее = “Write more neatly/carefully.” (correction: “be more careful than before”)

Why is there a comma before чтобы?

Because чтобы не делать ошибок is a dependent clause of purpose (“so that…” / “in order not to…”). In Russian, a clause introduced by чтобы is normally separated by a comma.

What does чтобы mean here, grammatically?

Чтобы introduces a purpose clause. The pattern is very common:

[Do X], чтобы [achieve Y / avoid Y].

Here: “Write more carefully so as not to make mistakes.”

Why is it не делать ошибок (imperfective) and not не сделать ошибок (perfective)?

Не делать ошибок uses the imperfective делать to mean “not to make mistakes” in a general/ongoing sense—avoid mistakes as a habit/process while writing.

Не сделать ошибок (perfective) would mean “not to make (any) mistakes” in a more one-time, result-focused sense (e.g., “in this particular text/test”). Both can be possible depending on context, but не делать ошибок is the most general “avoid mistakes” phrasing.

Why is ошибок in that form? Why not ошибки?

After делать in the meaning “to make (mistakes),” Russian typically uses the genitive plural:

делать ошибки is possible, but делать ошибок is very common, especially when meaning “make mistakes (in general / any mistakes).”

Also, with negation (не делать), genitive is especially natural: не делать ошибок = “not make mistakes.”

Is делать ошибки an idiom? Could you say совершать ошибки?

Делать ошибки is the most common everyday way to say “make mistakes.”
Совершать ошибки also means “make mistakes,” but it sounds more formal/bookish.

Why is there no word for you in the sentence?

Russian usually doesn’t need subject pronouns because the verb ending already shows the person. Пиши clearly signals “you (singular, informal).” Adding ты is possible but would add emphasis or contrast:

Ты пиши аккуратнее… = “You (specifically), write more carefully…”

What’s the difference between пиши and напиши in a sentence like this?

Aspect:

пиши (from писать, imperfective) = focus on the process / ongoing writing: “write (carefully).”
напиши (from написать, perfective) = focus on the result: “write it (and finish it).”

In advice about avoiding mistakes while writing, пиши is usually the natural choice.

Could the word order change? For example, Чтобы не делать ошибок, пиши аккуратнее?

Yes. You can move the purpose clause to the front:

Чтобы не делать ошибок, пиши аккуратнее.

Meaning stays basically the same; starting with Чтобы… puts more emphasis on the purpose (“To avoid mistakes…”).

Does аккуратнее mean “more аккуратный” as in “tidier,” or “more careful” as in “pay attention”?

In this context it mainly means more carefully / more neatly in your writing (handwriting, spelling, how you form letters, etc.). Depending on context it can also imply “pay more attention,” but with пиши it most naturally points to the physical/technical act of writing neatly and carefully.