To start with the level, clear the boxes on the bottom first — one of them contains a Rainbow Blast you should use on an apple or a pear. It will clear the rest of the boxes up top and fill the field up with pieces. Then you can start collecting the gnomes. Some boxes contain bombs, which will help you clear the field.
Save your power-ups to explode them simultaneously, as it lets you charge the Rainbow Blast faster and save some moves. The Rainbow Blast can be used to collect the remaining berries.