We describe a generic method, first presented in Ref.[1], to find inflationary solutions without the need to be specific about the scalar potential. The method shows that single-field models of inflation can be classified in two groups according to their predictions of inflationary observables, we call these groups as Class I and Class II. We apply the method to the study of different scalar potentials and compare their results with recent observational data. We conclude that potentials belonging to Class I are in better agreement with observations mostly because they can provide large enough values of the spectral index of linear perturbations.