Mixing

A couple of months ago I'd bottled a blueberry melomel and I've got a really tasty cherry melomel that finished a few days ago- or at least I figger it's finished. It's cleared out incredibly well and there aren't any bubbles coming out of the airlock.
Does anyone have any advice as far as mixing ratios goes? Just as a starting point, really.

I just wanted to put that guy in there for the fun of it

Tasting is the only way to get a decent blend. It's usually done when you have a few meads/wines that (although not bad) just don't suit your personal taste, adding a bit of sweet to dry, overpowering fruit tones to flavourless etc to balance. You need to be careful and put any blending experiments back under airlock just to make sure you don't start a re-ferment. If you're happy with both seperately i wouldn't bother mixing them.

Bananaphone!

I'm with Caplan. If you're happy with the taste, just rack em off, let em settle out, and bottle em.