First timer advice request

Hello everyone!

I've decided to dye a piece of my clothing for the first time and I want to ask a few beginner questions just in case to not ruin it. The piece is a 100% cotton hoodie that is a washed-down shade of black (the color is like this, it is not washed down in a sense that the color would be worn down); I would like to dye it to a darker shade. How should I do it to get the best results? What should I take in notice to not ruin it?

Thank You all in advance and have a great day!