\documentclass{article}
\usepackage{fontspec}

\setmainfont[Ligatures={Common,Historical,Contextual,Rare},Mapping=tex-text]{GaramondNo8}

\begin{document}
\noindent
Ligatures:\\
ff fi fl ffi ffl

\noindent
Smallcaps with Ligatures:\\
\textsc{ff fi fl ffi ffl}

\noindent
Sans ligatures:\\
f{}f f{}i f{}l f{}fi f{}fl f{}f{}i f{}f{}l

\noindent
Weird cases:\\
fff fffl fffi
\end{document}