Look, Im going to be real this is pretty easy for me because It's just the culmination of the last 10 years of things I've been learning. I don't have much advice since it just comes naturally to me. Don't be a perfectionist. Look things up. Ask questions. Get comfortable with not knowing how things work.
You should check out this tumblr post for more ideas for things to add.
To learn more HTML/CSS, check out these tutorials!