What I would do is look at a table of pKa values of various organic protons, e.g. carboxylic protons, alkynic protons, alpha-carbonyl protons, amine protons, conjugated proton sources, etc. Think of the properties of the anion and how well the resulting conjugate base can stabilize that anion (e.g. if anion is on a naturally electronegative species, if it is conjugated with pi-systems, etc.).
Flip those around to get basicity e.g. a stronger acid will be a weaker base, a hardly-acidic species will be very basic, etc.