Choose a color there is the many of on the board and concentrate on getting enough to bust one butterfly out of it's jar at a time.
If you can, try to collect the color blocks from one of the butterflies in the centre of the board first.
When that butterfly is gone it will open up the board more.
Use the color pop balloon/s (built up in the game) to help you collect the correct color and/or break the checkered pattern that the virus (spiky green balls) make.
Don't worry too much about the virus, other than to remove it when it gets into a large group (larger groups also help build up the booster)
Destroying blocks with the color pop, and when the butterflies leave, will both help level out the virus so it can be removed.