In a simple program, for example, you may wish to insert a blank line after your declarations, another after your initialization statements, another after your program reads its inputs, and another after the work is done before printing your outputs. In addition to the documentation header, your program should include other comments when appropriate. Each function you define ought to have an associated description, and some variables may require description beyond a simple name. If the behavior or purpose of a section of code is not obvious to the casual reader, you may wish to include some narrative about what's going on. As with all writing, be sure to use correct spelling, punctuation and grammar.
Programs are hard enough to read without having to account for illiterate programmers.