\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{graphs.standard}
\begin{document}
\begin{tikzpicture}
\graph[nodes={circle,draw},simple]
{
subgraph K_n [n=8,clockwise];
};
\end{tikzpicture}
\begin{tikzpicture}
\graph[nodes={circle,draw},simple]
{
subgraph K_n [n=8, clockwise] -> mid;
};
\end{tikzpicture}
\begin{tikzpicture}
\graph[nodes={circle,draw},simple]
{
subgraph K_n [n=8,clockwise];
};
\end{tikzpicture}
\end{document}