We believe and advocate that every member of this church should have a testimony of the divinity of the work; that he should know for himself, independent of any other person, that Jesus Christ is the Son of God, and that salvation is in him; that Joseph Smith is the agent and instrument through whom the knowledge of salvation has come again in our day; and that the mantle of the Prophet rests upon the President of the Church. By first gaining a testimony and then by being valiant in testimony, we can be heirs of salvation.
But no man can have a testimony of this work until he begins to get a knowledge of the gospel. A testimony is based on knowledge; first a man must learn about God and his laws, and then by obedience to these laws he will gain a testimony....We believe that all members of this Church should be fully and completely converted, so much so that they are changed from a natural and fallen state into Saints of God. But no one can attain unto such a state until he knows the laws that govern the process of being converted.
Elder Bruce R. McConkie, "Doctrines of the Restoration", Chapter 13, pg 223
I used to equate having a testimony to mere belief, to having one spiritual experience after another, thereby strengthening my testimony. In theory, then, the more spiritual experiences, the stronger my testimony.
Although that does and will solidify my testimony, that is not how to strengthen it. Spiritual experiences come because of testimony, not to create one. Without a testimony, spiritual experiences are few.
A testimony is the result of learning and living. Learning the word of God, learning His mission for each one of us. And then, living in accordance with that word and mission. Obedience.
The more we know and live, the more we want to obey, therefore, the stronger our testimony. That's why just mere reading of the scriptures will not help us progress very fast. We have to learn, have to immerse ourselves. Then live what we learn.