When I took AP English in high school, my teacher (I thank the heavens for her every day) told me to think about introductions as an upside down triangle. This is a representation of the graphic she showed the class:
Any time a student asks for help with introductions, I draw out this graphic because it helps me a tremendous amount in my own writing. I also tell students that even though introductions come first in the paper, they don’t have to be written first. It’s often quite helpful to not write the introduction until you’re entirely done with your paper. The most important aspect of the introduction is your thesis; with that, you can write your paper without even thinking about the introduction. Writing an introduction can be difficult because you’re not entirely sure what you’re going to write about until you do start writing. Start with the thesis, body paragraphs, or even conclusion and work from there. The writing process isn’t set in stone; there are multiple ways to approach academic writing.