How to take good pics or selfies?

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Hi ive been on instagram more frequently now and I have 152 followers but im not happy with my pictures. Im a teenage boy but I look so much younger than my age and all of my pictures are youngish. I also can't take a good picture or selfie to save my life. I can never pic a good pose , angle, or facial expression. I know to make sure you're in good lighting but when I do it still comes out bad. Do people really care how my pictures look? how can I make myself look older? and and how can i take better pictures and selfies?