  We investigate the predictions of inflation models with a non-minimal
coupling to gravity for inflationary observables such as the spectral index and
tensor-to-scalar ratio in a general setting. We argue that, depending on the
relation between the Jordan frame potential and a function characterizing the
non-minimal coupling, one can classify the model into three categories each of
which gives distinctive predictions for the inflationary observables. We derive
general predictions for each class and also investigate some explicit models to
discuss how the general features arise. Our results would be useful to design
an inflation model consistent with observational constraints with a non-minimal
coupling to gravity.
