Dominant Seventh Chord Inversions

Here is a great resource. At times I will refer to Drop 3s as Freddie Green chords. I would start with Drop 2 (page 2), a G7 in this example, followed by the Drop 3. Notice that you are moving the note on the 1st string down to the 6th string, same note 2 octaves below. 

We can write these out like this: (page 2)

Drop 3 - G7  G7/B  G7/D  G7/F

Drop 2 - G7/F  G7  G7/B  G7/D