Help for Ex commands is always listed with the colon included:
Help for settings is always listed with surrounding quotes, as Carpetsmoker already described:
Specific help files are listed by their file name:
:help undo.txt (cf.
Help for built-in functions is listed with trailing parentheses:
:help split() (cf.
Documentation for Vim's command arguments (i.e. those passed when invoking Vim from the shell) is listed with preceding hyphens:
:help -r (cf.
Help for subtopics within the documentation for various Vim features usually has an appropriate hyphenated prefix:
:help hl-Menu (cf.
:help syn-on (cf.
:help help-writing (cf.
Similarly, help topics within plugins generally use the plugin's name as a prefix:
Finally, something I didn't realise until I'd been using Vim for a while* is that the help includes topics for the default mappings in all modes.
Ctrl-v does something very different in Normal mode to what it does in Insert mode.
To get to the different topics, use the
v_ prefixes for Insert, Command, and Visual mode mappings, respectively, or no prefix for the Normal mode mapping:
* ...despite the fact that it's virtually the first thing you'll read if you type a plain
:help with no arguments! See "Get specific help" a few paragraphs down. (