ensoku no mae ni obentou no zyunbi wo site oita hou ga ii desu.

In normal Japanese writing, there usually are no spaces:

遠足の前にお弁当の準備をしておいたほうがいいです。

Textbooks and beginner materials often add spaces to show word boundaries more clearly. They are just a learning aid.

Here, の connects the noun 遠足 to 前.

• 遠足 = excursion / field trip
• 前 = before

So 遠足の前 means before the excursion.

A very literal breakdown would be something like the before of the excursion, but natural English is simply before the excursion.

In 遠足の前に, the に marks the time point before which something happens.

So:

• 遠足の前に = before the excursion
• 出かける前に = before going out
• 食べる前に = before eating

This is a very common pattern in Japanese.

This の also connects two nouns.

• お弁当 = bento / lunchbox
• 準備 = preparation

So お弁当の準備 means preparation for the bento or getting the bento ready.

Japanese uses noun + の + noun very often, and English can translate it in different ways depending on context:

• of
• for
• an adjective-like phrase

Here, preparation for the bento is the most natural idea.

Both are possible.

• 準備する
• 準備をする

Both mean to prepare or to make preparations.

So 準備をして is just the て-form of 準備をする. It is completely natural. You may also hear 準備して, which is also common.

〜ておく means to do something in advance or to do something and leave it done for later convenience.

So:

• 準備をしておく = to prepare it ahead of time

That nuance matters here. The sentence is not just saying prepare the bento. It is saying prepare the bento beforehand.

This is because of the grammar pattern 〜たほうがいい.

In this pattern, the verb normally appears in the plain past form before ほうがいい, even when the meaning is present or future advice.

So:

• しておいたほうがいいです = you should do it in advance
• not it was better that you did it

The た form here is part of the advice pattern, not a literal past-time meaning.

〜たほうがいいです means:

• it would be better to...
• you should...
• it’s advisable to...

It gives advice or a recommendation, not a strict command.

So 準備をしておいたほうがいいです means you should prepare it in advance or it’s better to get it ready beforehand.

In the expression 〜ほうがいい, ほう literally means side or option.

The が marks that option as the better one.

So the literal idea is something like:

• the option of doing X is good

That becomes natural English as:

• you should do X
• it’s better to do X

しておいたほうがいいです is a recommendation:

• you should
• it would be better to

しなければならないです is much stronger:

• you must
• you have to

So the original sentence sounds like friendly advice, not an obligation.

Japanese often leaves the subject unstated when it is obvious from context.

In this kind of sentence, the implied subject is usually:

• you
• or one in a general sense

So the sentence naturally means something like:

• You should prepare the bento beforehand
• It’s best to prepare the bento beforehand

The listener is understood without being said directly.

いいです is the polite form.

Compare:

• しておいたほうがいい。 = plain / casual
• しておいたほうがいいです。 = polite

So the sentence is polite, but still very common and natural in everyday speech.

In this word, お弁当 is the normal everyday form. Even though お is historically a polite prefix, for this word it is usually treated as part of the standard vocabulary.

• お弁当 = normal and natural
• 弁当 = possible, but less neutral in many situations

So in most cases, learners should just remember the word as お弁当.