is derived from the Coronation street character
Liz McDonald, who frequents tarty clothes, suitable for a younger generation, maybe
15 years ago. She wears lots of make up, and her trademark is a gold "L" around her neck.
"Lizzin it up" therefore means basically
to put on a lot of makeup and/or dress up in a way similar
to Liz. However, as of late it has been used to describe any kind of preparation before going out on the town.