How does somebody develop spiritually?

It's all in the mind! There is no such thing as developing spiritually. Some think that belief in religion makes them more spiritual but this is bunkum! My nearest guess would be wisdom through maturity and objectivity.

Thru prayer and meditation of the Bible.

Constructive discussion. Avoid deconstructive people at all costs (at first) because it will lead to a lot of confusion. Find someone you trust that you can learn from. Read a lot of books with a lot of different points of view.

I think it's when people hit Rock bottom
and they are at the end of their rope.

However, then they choose to live by God rule of life.

By finding themself. This is done by forgetting about everything going on in your life. Picture yourself a drop of water in the ocean that is life.

Take a day off and go lay in the grass and gaze at the clouds, take your shoes off.

Pick a night to go back out and do the same thing and look at the stars.

Take a look at yourself and look at the big picture. How did we get there? What does this mean to you. Find out if you're spiritual in your belief of a God, or if you independently develop your own gravitation towards a certain belief system.

If you only use religion as a method to get through rock bottom... it's understandable, but... it's a crutch rather than something that's a part of you... spiritually.

meditate for a while...just sit somewhere quiet for 10 minutes a day...think about your spirit or ask questions and just wait..the more you do it the more questions you will answer about your spirituality

Study more than one "religion" and see if one suits you. If not, and I know how lame this will sound, but a well-known teacher recommended constantly trying to answer the question "Who am I?".
Jesus said "It is by your faith that ye are saved", but what if you have no faith? Have faith in yourself!!
Buddha said something like "Do not believe on the strength of tales of old, do not believe what many tell you to, after investigation believe that which you, yourself have found to be true."
There are a lot of naysayers, so I'm really going out on a limb BUT try repeating the mantra Om Namah Shivaya. What it means is less important than the soothing, strengthening effect it will have on your mind. One or twenty times aren't enough, you develop more as you say more; do 3 pushups qualify you for the Olympics?
Good luck, don't quit!!
Love thy neighbor is a place to start, too. It doesn't require religion or faith.

Remembering God, practicing His commands, expressing thankfulness to Him for Divine Guidance, Meditating on the sacred verses, bearing hardship for the service of mankind, detachment of all things save God...and lots of other things deriving from the above.

When you do not develop it.

study is one way but staying open to life's experiences is the best way to grow spiritually ( imho)

spirituality isn't limited to just "God" and people say "God" as if they have any friggin idea what the hell theyre talking about. a person could develop spirituality in a number of ways it just depends on what is more suitable to the entity searching for truth. You could be looking or you could just stumble upon it for higher reasons, maybe your life is going down the wrong path and you need to change but are too stubborn. something could happen to you something good or bad thus changing your outlook on life. or you could try a psychedelic or some sort of drug for the first time. that could also help alter your current perception on things. so please define your question.. are you looking to find and develop spirituality or are you looking to currently further your understanding?

You jut do- It takes time of development in finding and growing and realizing hes better than anything anywhere and thats all.