The main thing is to pray the rosary daily. It is such a powerful tool against the devil and against temptation to sin. Certainly, some days are just naturally associated with some mysteries, such as Friday with the Sorrowful and Sunday with the Glorious mysteries. That being said, the suggested mysteries for each day are just that; suggestions. By assigning days to the mysteries, it allows us to remember all of them throughout a one week cycle. I have even been at funeral rosaries where the priest leading the prayers selected mysteries from several different themes (i.e., The Annunciation, The Institution of the Eucharist, The resurrection, etc) Again, the main thing is to remain faithful to prayer.