\documentclass{article}

\begin{document}

\begin{itemize}

  \item Lists with items on one line

  \item Lists with items
    on multiple lines

    % comments before a list item
  \item Another item

  \item Another item
    % comments inside a list item
    Or even just % trailing comments

  \item Every
  \item should start
  \item a new line

\end{itemize}

\begin{myitemize}

  \item Custom list environments can be specified in the configuration file.

\end{myitemize}

Commands such as itemsep should not be affected.
\setlength{\itemsep}{0pt}

\end{document}
