If the include is for a non-obvious reason, the reason should be commented. In most cases, system include files like stdio.h should beincluded before user include files. Any defines and typedefs that apply to the file as a whole are next. The functions come last, and should be in some sort of meaningful order. Like functions should appear together.
Considerable judgement is called for here.
If defining large numbers of essentially-independent utility functions, consider alphabetical order.