saki ni yomu ni koshita koto wa nai.

It is best to read first.

Breakdown of saki ni yomu ni koshita koto wa nai.

• 読よむ: to read
• 先さき に: first
• 〜に 越こした こと は ない: it is best to; nothing is better than

Questions & Answers about saki ni yomu ni koshita koto wa nai.

What does 先に mean here?

先に means first, beforehand, or ahead of time.

• 先 = ahead, previous, earlier
• に turns it into an adverbial expression

So 先に読む means read first or read in advance.

Exactly how you translate it depends on context:

• read it first
• read it beforehand
• read ahead

Why is there a に after 先?

In 先に, the particle に is making 先 function adverbially.

This is very common in Japanese. It is similar to saying:

• 早めに = early
• 前に = before
• 後で = later / afterwards

So 先に is not a separate mysterious grammar point here; it is just the normal way to say first / beforehand.

Why is there another に after 読む?