The parskip command makes a skip between paragraphs. The length of skip can be set using the command \setlength, e.g.,

\setlength{\parskip}{15pt plus 1pt minus 1pt}

The command \itemsep sets the space between items in lists, e.g.,

\begin{itemize}
\itemsep = 0.8cm
\item 
\end{itemize}

The command \doublespace makes lines after this command double spaced. This is convenient to produce PDF document for review.