Хорошая орфография и точная пунктуация помогают писать так, чтобы тебя понимали.

Because each adjective agrees with its own noun:

• хорошая goes with орфография
• точная goes with пунктуация

Both орфография and пунктуация are feminine singular nouns, so their adjectives are feminine singular too.

Even though the whole subject is made of two things joined by и (орфография и пунктуация), each adjective still matches only its own noun.

Because the subject is actually two things:

• Хорошая орфография
• точная пунктуация

They are joined by и, so together they form a plural subject. That is why the verb is помогают rather than помогает.

Compare:

• Хорошая орфография помогает. = Good spelling helps.
• Хорошая орфография и точная пунктуация помогают. = Good spelling and accurate punctuation help.

They are in the nominative case, because they are the subject of the sentence.

You can tell because they are the things doing the helping:

• Хорошая орфография
• точная пунктуация

These two together are what help.

After помогать (to help), Russian often uses an infinitive to say help to do something.

So:

• помогают писать = help [someone] write / help with writing

This works much like English:

• They help write
• They help you write

Russian often leaves out the person being helped if it is general or obvious from context.

Russian often leaves out an indirect object like you if the meaning is general.

So помогают писать can mean:

• help one write
• help you write
• help people write

The sentence is stating a general truth, so there is no need to say тебе explicitly.

If you wanted, you could make it more explicit in some contexts, but the original version sounds natural and general.

Так, чтобы means something like:

• in such a way that
• so that
• in a way that

So this part:

• писать так, чтобы тебя понимали

means:

• to write in such a way that people understand you
• to write so that you are understood

It is a very common Russian structure.

Because чтобы introduces a subordinate clause.

Here the sentence has:

• main part: Хорошая орфография и точная пунктуация помогают писать так
• subordinate part: чтобы тебя понимали

Russian normally puts a comma before чтобы in this kind of structure.

So the comma is required.

Тебя is the accusative form of ты here.

In the clause:

• чтобы тебя понимали

the verb понимать takes a direct object, and you are the person being understood. That makes тебя the direct object.

So:

• кто-то понимает тебя = someone understands you

That is why it is тебя, not ты.

Because тебя is not the subject. It is the object.

The subject is left unstated and is understood as people in general:

• чтобы тебя понимали = so that people understand you

Russian often uses the 3rd person plural with no explicit subject to mean people / others / they in a general sense.

So the plural verb does not refer to you. It refers to unspecified people who might read what you write.

This is a very important pattern in Russian.

After чтобы, Russian usually uses the past-tense form of the verb, but the meaning is not necessarily past. It often expresses:

• purpose
• desired result
• something hypothetical

So:

• чтобы тебя понимали

does not mean so that they understood you in the past It means:

• so that they understand you
• so that people will understand you
• so that you are understood

This is just how чтобы works grammatically.

Because понимали is imperfective, and that fits the general meaning better.

• понимали = understood / were understanding / would understand, in a general or ongoing sense
• поняли = understood successfully, as a completed result, usually in a more specific situation

Here the sentence is about writing clearly in general, so that readers understand you as a continuing outcome. That makes понимали the natural choice.

If you said чтобы тебя поняли, it would sound more like:

• so that they would understand you (on this particular occasion)

That is possible in other contexts, but the original sentence is broader and more general.

Yes. Very often English would naturally translate it with a passive:

• so that you are understood

But Russian does not use a passive form here. Instead, it uses an impersonal/general 3rd person plural:

• people understand you
• literally: so that they understand you

This is extremely common in Russian and often sounds more natural than a passive construction.

Yes, Russian word order is flexible, but the original order is natural and clear.

The sentence starts with the subject:

• Хорошая орфография и точная пунктуация

then the verb:

• помогают

then the infinitive phrase:

• писать так, чтобы тебя понимали

This order works well because it presents:

1. what helps
2. what it helps you do
3. the intended result

Other word orders are possible, but this version is smooth and standard.

Very literally, it is:

• Good spelling and accurate punctuation help write in such a way that they understand you.

A more natural English version is:

• Good spelling and accurate punctuation help you write so that people understand you.
• Good spelling and accurate punctuation help you write clearly enough to be understood.

So the grammar is more literal than the smooth English translation, but the underlying structure is straightforward once you break it into parts.