How do I change column or row separation in LaTeX tables?

\setlength{\tabcolsep}{20pt}
\renewcommand{\arraystretch}{1.5}

\documentclass{article}
\begin{document}

\section*{Table with default spacing}

% A table with default row and column spacing
\begin{tabular}{ l c c }
First Row & 6 & 5 \\
Second Row & 4 & 10\\
Third Row & 20 & 30\\
Fourth Row & 100 & 30\\
\end{tabular}

\section*{Table with adjusted spacing}

% A table with adjusted row and column spacing.

% \setlength sets the horizontal (column) spacing
% \arraystretch sets the vertical (row) spacing

\begingroup

\setlength{\tabcolsep}{10pt} % Default value: 6pt
\renewcommand{\arraystretch}{1.5} % Default value: 1
\begin{tabular}{ l c c }
First Row & 6 & 5 \\
Second Row & 4 & 10\\
Third Row & 20 & 30\\
Fourth Row & 100 & 30\\
\end{tabular}

\endgroup
% The \begingroup ... \endgroup pair ensures values of spacing 
% parameters only affect this particular table, and not any
% subsequent ones in the document.
\end{document}