There are chords you can practice to strengthen your ring and pinky. The G major chord is pretty good, since you can use your middle, ring and pinky for the three finger version. Power chords, two string versions you can use either your ring or pinky and three string versions use both.

There are some riff that you can use to help, especially if you assign certain frets to certain fingers while practicing the riffs. Smoke on the Water is a good one for this: third fret is pointer, fifth fret is ring, and sixth fret is pinky. (Note: for the single note version not the power chord version, although you can use the power chord version to strengthen your fingers too.)