It is becoming more and more obvious to me, that Catholics have it very lucky. We have many devotionals, prayers, etc, that we can use to help us to attain a relationship with God and allow us to tap into His mercy and His life-saving grace. To me, if you were to choose two, and only two of these, the choices would be obvious. The Rosary and the Holy Scriptures.
The Rosary was given to us by Our Holy Mother herself. She even promised that those who have a devotion to her Rosary and pray it daily would receive 15 Graces for doing such. The best (in my opinion) grace is the ability to spot heresy. Heresy is rampant in today’s world, but being able to see it and call it out for what it is is a tremendous blessing and grace in and of itself. The Rosary in its entirety is 15 Decades long. There is nothing wrong with praying only 5 decades a day, but if you can work yourself up to 15, that is great and graces will pour down upon you.
The Bible is the word of God. When you read the Scriptures, especially the Gospels, you will know Jesus Christ. You will know His teachings and the way He thinks. You will also learn why Holy Mother Church does what she does. I would suggest reading for 15 minutes a day if you can (if you read for 30 minutes you can get a plenary indulgence). St. Jerome once wisely said “ignorance of scripture, is ignorance of Christ”. This is very wise words of wisdom.
If you do not know what Jesus has said in the Scriptures, then you will not know what His teachings are. A good Catholic bible would be Douay-Rheims, a RSVCE, or even a New American Bible. Do not use the King James Version or any Protestant bible. The KJV and all Protestant bibles have books removed from them, so they are not complete. They will also intentionally translate verses incorrectly in order to fit their point of view as well as their beliefs.
Your Catholic faith will grow tremendously by doing these two devotions, praying the Rosary and reading Scripture daily.