Journe Website Mockup

This shot is my first big website design for a client! Super fun! The website is up and it's super fun to see! However, I had sent it to a developer to code and there are a lot of things he didn't get right with spacing and sizing of elements and text. Anyone that has advice on how best to communicate your designs with a developer? Like what info do they need specifically from me other than the design itself and all the files and elements?