to agree; to decide upon; to enter into (a contract)
双方が条件を取り決めた。
Both parties agreed on the conditions.
細かなルールを取り決めている最中だ。
We are in the process of deciding on the detailed rules.
契約前に支払い方法を取り決めることが大切だ。
Settle on a payment method before signing a contract.