Watch the Add Rhythm and Groove online guitar lesson by Ravi from 1-2-3 Songwriting
Add some rhythm and groove to your new section. Your riff probably already has a natural groove to it, so go with that and create a complimentary rhythm for your chord progression. Now is a good time to decide if your chords are more likely to be your chorus or verse. If you think it will be for the chorus, make sure it feels even bigger than your riff. Alternatively, if your riff screams chorus (and ultimately is the main hook in your song), lay back a little with the chords so your chorus will pop with the riff. In my song, the chords will be my chorus. Figure out what works for your song, come up with a good rhythm, and check it of your list.