Step by Step
To begin the practice of self-inquiry, sit for meditation as usual. If you don't already have a regular practice, just sit quietly and allow the mind to settle naturally. Don't attempt to focus your mind or manipulate your experience, just rest as awareness itself.
After 10 or 15 minutes introduce the question "Who am I?" Drop the question into the stillness of your being like a pebble into a still forest pool. Let it send ripples through your meditation, but don't attempt to figure it out!
When the pond is tranquil again, drop in another pebble and see what happens. Set aside any conceptual answers, such as "I am a child of God" or "I am consciousness" or "I am a spiritual being of light," and come back to the question. Though true at a certain level, these answers will not satisfy your hunger for spiritual sustenance.
Instead of "Who am I?" you may prefer asking, "Who is thinking this thought? Who is seeing through these eyes right now?"
For the practice of self-inquiry to work its magic, you must recognize at some level that the word I, though superficially referring to the body and mind, actually points to something much deeper.
Let your inquiry be earnest but effortless, without tension or anxiety. Here's a hint: You definitely won't find the answer in the file folders of spiritual beliefs you've amassed over the years, so look elsewhere, in your actual, present experience.
Eventually, the question "Who am I?" reveals the answer, not as a thought or a particular experience but as a vibrant, timeless presence that underlies and infuses every experience.