One of the typical problem by using beamer class are tables respectively showing tables. If they are to big to be shown on one frame there are two possibilities to solve this problem.
Frist, use the plain option at the frame where you want to set the table
\begin{frame}[plain]
\frametitle{a table is to big}
\begin{table}
\begin{tabular}{|r|c|l|}
\hline
test 1 & test 2 & test 3\\
\hline
A & B & C \\
\hline
\dots & \dots & \dots \\
\hline
\end{tabular}
\end{table}
\end{frame}
By using plain you just get a little bit more space to fill.
Second, just change the font size within the table:
\begin{frame}
\frametitle{a table is to big}
\begin{tiny}
\begin{tabular}{|r|c|l|}
\hline
AAA & BBB & CCC \\
\hline
111 & 222 & 333 \\
\hline
\end{tabular}
\end{tiny}
\end{frame}
Now the font is tiny and has a size of 6 pt because normalsize is 11 pt.
An overview about the size and commands you will find here even for other documentclasses.