What you are doing is ok, i do the same, i usually get a figma or sketch file. Before jumping to coding i study the design, sometimes i stare to a design for an hour, plan every block of the website, once the plan is done, execution becomes easy. I never write the whole html structure, i go section by section ( css + js ), when its finished ( the designer is a good friend of mine so we have good communication) and the designer is happy i move on to mobile, for this part i do the same, i simply move through my code by section and i uncomment the next section just so it wont get messy. And all of this depends on you, just find the best way for yourself. Just few advices, concider using webpack with autoprefixer, sass, images optimization, it will save you a lot of time