I remember we used to sing this song way back in Sunday School:
If you want to grow 2x
Hallelujah read your Bible pray every day, pray every day, pray every day
read your Bible pray every day If you want to grow
This song reminds us of what to do as children of God if we want to develop our spiritual life. You can develop your spiritual life when you are committed to a personal daily devotional life through the study of the word of God, effective prayer life and fellowship with the brethren (e.g. Sunday service, Small Discipleship Group/Home Cell Meetings, etc.). To develop your spiritual life, you need to study the Word of God intentionally.
Scripture encourages us to desire the sincere milk of the Word that we may grow thereby, because it is the Word of God that is able to build us up (1 Peter 2:2, Acts 20:32). You know you are developing your spiritual life when you begin to bear fruits and this is only possible when you delight yourself in the study of the word of God (Ps. 1:2-3). When you know the word of God, you have a solid foundation upon which you can develop and grow your spiritual life. The knowledge of the word of God brings depth to your spiritual life, helps you to discern false teaching, and gives you power over temptation and sin.
Another important key to develop your spiritual life is prayer. When prayer is consciously practiced, it transforms your very being, bends you towards the will of God and subjects the desires of the flesh, which are the greatest hindrances to your spiritual development under your control. Without this activity, there is no sincere communication between the Christian and God, and if there is no communication, there would not be any proper spiritual development since it is one of the spiritual nutrients to Christian growth.
In this discussion, the final tool to develop your spiritual life is fellowship with the brethren. The scripture admonishes us in Hebrews 10:25 not to neglect assembling together as believers. This is because no matter where we are in our faith, fellowship provides us with strength in the Lord. Attending church meetings and being in the small discipleship group gives you the chance to learn and grow in the faith since the weaker ones will be encouraged by the mature ones.