Ever since Xcode 5 added native support for doxygen, it really pays to annotate your code with doxygen style comments, which only require a few extra characters to comments you may already make.
In looking for tips and tricks, I turned up an excellent how-to written 4 years ago (but still correct) that offers many different techniques. For example, you can remind yourself (and others) how to use a particular variable:
@property(assign) int ts; ///< Short Comment
or line wrap for up to 3 lines of comments:
@property(assign) int ts; ///< Set the complete ... ///< the progress ...
If you’d rather use C-style comments you can:
@property(assign) int ts; /**< Set the complete ... the progress ... */
The parser seems really smart about how finding continuation comments and also ignoring leading white space. In my examples, I indented the second lines, but you can leave them pegged to the left margin if you prefer.
The more common doxygen usage is to provide annotation blocks above methods, and the oodles of options you can use to do that can be found in this recent post on StackOverFlow (make sure to upvote the question and answer!):
You can add this handy code snippet to your Xcode Code Snippet library:
/** <#description#> @param <#parameter#> @returns <#retval#> @exception <#throws#> */
as detailed here (and I just did!):
From then on you and others can get help during autocomplete, as well as by option-clicking on a method. I was slow to start using this, but now its getting to be second nature.