Learn Hardcore Japanese: kantanna rensyuumondai wo mainiti suru to, nihongo no kaiwa ga siyasui desu. - If you do simple practice exercises every day, conversations in Japanese become easier.

The verb before と is in a subordinate clause (the “if/when” part), and it is very common—and natural—to use the plain (dictionary) form there:

雨が降ると、寒いです。
仕事が終わると、うちへ帰ります。

Politeness is carried mainly by the final clause of the sentence:
日本語の会話がしやすいです。 (polite, because of です)

So mixing plain form in the conditional clause (すると) with a polite main clause (しやすいです) is normal and polite in Japanese.

What exactly is と doing here in 毎日すると、日本語の会話がしやすいです?

Here と is the conditional と, meaning roughly “when/if A happens, B (naturally) happens.”

Pattern:

A（plain form）と、B。
→ “Whenever/when A, B (as a natural result).”

In this sentence:

A = 簡単な練習問題を毎日する
B = 日本語の会話がしやすいです

So it means: when you do simple practice problems every day, as a natural result, Japanese conversation is easy to do.

Compared to other conditionals:

〜たら: more general “if/when,” often for one-time situations.
〜ば: more hypothetical or formal.
〜と: often used for regular, automatic, or natural results (like cause-effect rules).

Does 毎日 modify する? Could it go in another place?

Yes, 毎日 is an adverb of time modifying する (“to do [them] every day”).

The word order is quite flexible. All of these are natural:

簡単な練習問題を毎日すると
毎日簡単な練習問題をすると
毎日、簡単な練習問題をすると

Japanese adverbs like 毎日, よく, たくさん etc. can usually appear before the verb phrase, and often before the object as well.

What does 日本語の会話 literally mean? How is it different from just 日本語?

日本語の会話 is literally “conversation of Japanese”, i.e. “Japanese conversation / conversation in Japanese.”

日本語の会話 → “Japanese conversation” (conversation that is in Japanese)
Just 日本語 → “the Japanese language” in general (speaking, reading, etc.)

You could also say:

日本語での会話
日本語で会話すること

But 日本語の会話 is a natural, compact way to say “Japanese conversation” as a noun phrase.

Why is が used in 日本語の会話がしやすいです and not は or を?

Here が marks the subject of the adjective-like word しやすい.

The pattern is:

X が V-やすいです。
→ “X is easy to V / it’s easy to do X.”

Some examples:

この本は読みやすいです。
→ “This book is easy to read.” (この本が読みやすいです is also OK)
パソコンが使いやすいです。
→ “The computer is easy to use.”

In this sentence:

日本語の会話がしやすいです。
→ “Japanese conversation is easy to do.”

Why not は?

日本語の会話はしやすいです is also possible.
- が focuses on “Japanese conversation” as the thing that is easy.
- は would make it the topic (“As for Japanese conversation, it is easy…”), slightly more contrastive.

Why not を?

With V-やすい, the noun that would normally be the object of the verb becomes the subject of やすい, so it takes が (or は), not を.

What does しやすい mean, and how is it formed?

しやすい comes from the verb する + the auxiliary やすい.

Pattern:

Vます-stem + やすい
- 読む → 読みやすい (easy to read)
- 使う → 使いやすい (easy to use)
- 行く → 行きやすい (easy to go [there])
- する → しやすい (easy to do)

やすい here is an i-adjective that attaches to the verb stem and means “easy to do (that verb)”.

So:

日本語の会話がしやすいです。
≈ “Japanese conversation is easy to do.”
(or more natural English: “It’s easy to have conversations in Japanese.”)

Could you say 日本語の会話をしやすいです instead of 日本語の会話がしやすいです?

No, 日本語の会話をしやすいです is ungrammatical.

Reason: with V-やすい, the thing that would be the object of the original verb becomes the subject of やすい.

Original: 日本語の会話をする → “to do Japanese conversation”
With やすい: 日本語の会話がしやすい → “Japanese conversation is easy to do”

So the noun takes が (or は), not を. Parallel examples:

このペンで字を書く。→ 字が書きやすい。
その映画を見る。→ その映画が見やすい。

Using を with 〜やすい is not the normal pattern.

Could you say 日本語で会話しやすいです instead? Is that different from 日本語の会話がしやすいです?

Yes, 日本語で会話しやすいです is also natural, and the nuance is slightly different:

日本語の会話がしやすいです。
- Focuses on “Japanese conversation” as a noun.
- Literally: “Japanese conversation is easy to do.”
日本語で会話しやすいです。
- Treats 会話する as a verb: “to have a conversation.”
- 日本語で marks the language/means: “in Japanese / using Japanese.”
- Literally: “It’s easy to converse in Japanese.”

In English, both are often translated similarly (“It’s easy to have conversations in Japanese”), but structurally:

X が V-やすい (noun + が + V-やすい)
XでVしやすい (adverbial X + Vしやすい)

Why doesn’t the sentence have a clear topic with は (like 私は)? Is that okay?

In Japanese, the topic is often omitted when it is clear from context.

Possible fuller versions could be:

（あなたが）簡単な練習問題を毎日すると、日本語の会話がしやすいです。
→ “If you do simple practice problems every day, Japanese conversation is easy (for you).”
（日本語は）簡単な練習問題を毎日すると、日本語の会話がしやすいです。

But since the sentence is making a general statement or advice, leaving out an explicit topic like 私は / あなたは is natural and normal.

So yes, having no explicit は-topic here is perfectly fine.