しとくto do in advance, to do as a preparation

妻(つま)が風呂(ふろ)にいる間(あいだ)に掃除(そうじ)をしとく。

I'll clean up in advance while my wife is in the bath.

プロポーズの前(まえ)に薔薇(ばら)の花束(はなたば)を注文(ちゅうもん)しといた。

I ordered a bouquet of roses in advance before the proposal.

タクシーを事前(じぜん)に手配(てはい)しといたら社長(しゃちょう)に褒(ほ)められました。

I was praised by the president because I had arranged for a taxi in advance.

妻(つま)が夫(おっと)に：「あなたが寝(ね)ている間(ま)にもう洗濯(せんたく)をしといたわよ！」

My wife said to her husband: 'I already did the laundry while you were sleeping!'

結婚式(けっこんしき)の前(まえ)にダイエットをしといてよかった…おかげで写真(しゃしん)写(うつ)りがいい！

I'm glad I did a diet in preparation before the wedding... Thanks to that, I look good in photos!