It is obligatory to act upon the covenant (ahd) with Allah almighty. If one does not do so it is a sin and a kaffarah must be given. Whereas, it is not obligatory to act upon the promise (wa’d) and there is no kaffarah for doing so. It is better not to do either of them. Doing good deeds when possible and avoiding bad deeds when possible is better than obligating oneself with additional religious duties.
For a person who missed a full days' prayer, it is recommended to make them up in the order that they were missed. For a person who missed Maghrib and Isha prayers, or missed Dhuhr and Asr prayers, the first prayer must be made up first.