By applying the formulas for seventh chords to the C major scale, the following series of chords is created. These are called scale tone seventh chords. If you analyze the notes of these scale tone 7th chords, you will notice that they are all based on the C major scale tone triads and each one has another 3rd interval added above it.
It is essential to be able to play these scale tone 7th chords as arpeggios in all five forms on the fretboard, and in all twelve keys. Here is an example in C major. Learn it from memory in the open position and then work out the other fingerings as well as transposing it to all the other keys.