LaTeX formatting issues

I am about to submit an article for review, and had to format in a special way. Here is a quick summary of what I did:

No paragraph indents:

\setlength{\parindent}{0in}
but a single line between:
\usepackage{parskip}
Left text justification:
 \begin{flushleft} ...  \end{flushleft}
Double spacing:
\renewcommand{\baselinestretch}{2}