Seeing all these first Far Side pieces pop up is making me nostalgic, so here's the stuff I wish someone had told me before I stitched my first Larson panel years ago. Dense single-colour areas like a dinosaur body or a night sky will destroy your tension if you just keep stitching in one direction. Break the area into small sections and alternate your direction every few rows, otherwise the fabric puckers and no amount of blocking will fix it afterwards.
Use two strands of floss, not three, even though it feels slower. You get way better coverage with less bulk and the outlines stay crisp, wich matters when the whole joke depends on the drawing reading clearly at arm's length. For the lettering, backstitch is fine but stem stitch looks so much better on a curved caption. It also holds up when the piece gets framed. Speaking of which, mount the fabric on a stiff backing before it goes anywhere near a frame, beacuse embroidered panels sag in a hoop-only frame within a year.
Last thing, sketch the panel on the fabric with a water soluble pen and check it from across the room before you commit. Larson's jokes work because of timing and composition, and if the composition is off the stitching won't save it.