Tones of practice :) .. You could also go to college to sharpen your skills which I urge you to do! However, you should start with the link below.
tirelessly look at the works of the greats. Try to copy them. You will learn the process that one with "vision" has to go through to produce good photographs. Once you have gotten enough confidence in yourself, go work for those already established in the field and learn from them.
By loving the art form, by committing to it with all your energy and passion, by having incredible desire to follow your inter calling and purpose and knowing that God gives us all a mission which has a purpose, if we follow this inter calling we will be in tune with the universe.
We all have in our own small efforts and significance make tremendous impact on many of our fellow humans that appear in our time line here on earth. Commit to it and so many will benefit even more than you do.
Start by exercising your ability to see the world around you. You've seen people hold up their thumbs and fingers to create a frame and that's where to start. Looking through the camera you are putting a frame around what you think is interesting.
A cellphone camera is a useful tool so start using it. Find a place online to show the world (and other photographers) which of your images you find interesting and start talking about why you like the image. At this point you are indulging in a hobby. To understand the technology of photography you will need the formal education found in school so do some research to find a good learning environment. When you have developed a collection of photographs that demonstrate your skills and interest, show that work to professional photographers and ask about assisting them. They don't always pay but you have a lot to gain from the experience. By this time you should know what field of photography you want to pursue so start searching for employment in that field. Magazines, websites, newspapers, advertising, catalogs, portrait studios and even art galleries employ photographers. Most photographers eventually start their own business so you'll need to study business and marketing among other things. Remember when you are self-employed, you are always searching for the next assignment so learn how to network with professionals in your chosen field.
That is my answer to your question and now comes my opinion. Go for what you love! It could be people, sports, fashion, social and cultural events, news, art, architecture, science, nature, education... You get the idea. Your best photographs will come from the subject you are most passionate about.