Common Latex mistakes

Using underscores eg. hello_world should be hello\_world
cutoff > 0.8 to $cutoff > 0.8$

Working with tables:
\usepackage{longtable}


\begin{center}
\begin{longtable}{|c|p{3cm}|p{6cm}|c|}
\caption{
\bf{my table title}} \\
%table information
\hline
1 & 2 & 3 & 4 \\ \hline
a & b & c & d \\ \hline
\end{longtable}
\begin{flushleft} my table caption
\end{flushleft}
\label{tab:label}
\end{center}