To create a bigger sound, it is common to double one of the notes of a triad, thus creating a four note voicing. Two common four note voicings are shown in the following diagram along with an example demonstrating a guitar part created from them.
To change between these chords, all you need to do is play the D chord and then place the second and third fingers ahead of the first finger bar to form the G chord, as shown in the third diagram here.
The first two bars of this example alternates between the two chords shown previously and then moves down two frets where the chord shapes become C and F. Try making up your own parts using these chords. Don’t forget to transpose them to all the other keys.