I do it like that (sight of a one man team ^^):
(rough overview)
-write a small gdd to know the goals and the rough outlines
-start prototyping the most important gameplay features -> you will need them for the level
-after that start with the asset creationg + with the map
-finalize the gameplay
-polish the map and assets
-get some people that test your game
-improve more stuff
-release it