When changing between the C and D7 chords, do not move your first finger, as it is common to both chords. The first finger acts as a pivot around which the other fingers move. This will make the chord changes easier.
Practice slowly and evenly and count or tap your foot as you play to help you keep time.
There are four beats in each bar. When strumming, only your wrist should move. Do not move your arm and keep your forearm resting on the upper edge of the guitar. Remember to keep your left hand fingers just behind the fret. If you place a finger on top of the fret, the note will sound deadened. If you place it too far back from the fret, the note will buzz and you will have to press down harder to prevent this from happening. If you have an acoustic guitar, play the strings over the sound hole as this results in the best sound.
G7
To play the G7 chord, place the first, second and third fingers of your left hand as shown in the diagram. Strum all six strings.
The following chord progression contains all three chords you have learned so far. Use the pivot finger when changing between C and D7.
This chord progression contains two chords in each bar. Each chord sounds for two beats.