Watch the Using the ii V online guitar lesson by Jason Loughlin from Rockabilly Survival Guide: Lead
The ii V is the most common turnaround in swing. It's purpose is to create anticipation and momentum into the next chord. Using it definitely leans towards the more sophisticated side of rockabilly improvisation but players like Hank Garland and Brian Setzer have always incorporated it in this solos. I'll show you to outline ii V triads and develop some template patterns to work off of.