まず

Like many other adverbs in Japanese, まず can be used to modify a whole phrase/sentence. This means that it will regularly appear at the beginning of a statement. まず is associated with kanji 先(まず) and therefore carries the meaning of 'first', or 'starting with'.

• まず宿題(しゅくだい)をしたほうがいい。
  First, it would be best for me to do my homework.
• まずエンジンをかけて。
  First, please turn on the engine.

まず is regularly used when you want to convey that something 'should' be done before anything else/discussed first, and not when something is first in rank.

• 赤(あか)い車(くるま)がまず、ゴールをしました。
  The red car finished to start with. (Unnatural Japanese)

In this kind of sentence, it would be far more natural to use a statement like 一番(いちばん), 最初(さいしょ) or 一位(いちい) if discussing rank.