Ada '83 Quality and Style:

Guidelines for Professional Programmers

Use consistent spacing around delimiters.
Use the same spacing as you would in regular prose.
Indent and align nested control structures, continuation lines, and embedded units consistently.
Distinguish between indentation for nested control structures and for continuation lines.
Use spaces for indentation, not the tab character (Nissen and Wallis 1984, w2.2).
Align operators vertically to emphasize local program structure and semantics.
Use vertical alignment to enhance the readability of declarations.
Provide at most one declaration per line.
Indent all declarations in a single declarative part at the same level.
Align parameter modes and parentheses vertically.
Use blank lines to group logically related lines of text (NASA 1987).
Highlight the top of each package or task specification, the top of each program unit body, and the end statement of each program unit.
Start each statement on a new line.
Write no more than one simple statement per line.
Break compound statements over multiple lines.
Adhere to a maximum line length limit for source code (Nissen and Wallis 1984, 2.3).