When running a fluorocarbon leader, what is the common length that you use????   I am just starting to get into running some fluoro leaders on some of my braid rods.  I am currently playing around with some around 18-24 inches.  Is that sufficient???

I generally use a leader a little longer than the rod it's on, in other words on 7' rod I'll use about an 8' leader.

I fish super-clear water, and I know a lot of guys use a shorter leader than that, similar to what you're using.

The longer leader also gives me more to use when tying knots from switching baits or if a few inches near the lure is getting nicked.

Since I'm often pitching baits in sparse cover an clear water, I use a fluoro leader and braid mainline.  Usually 40-65# braid (Daiwa Samurai), with a 15# or 20# fluoro leader (in case I get in some nasty cover throughout the day).

My leaders are always initially just an inch shorter than the distance from reel to tip.  This ensures the knot (alberto) is not going to run through any of the guides, especially the tip, when making a precise pitch.  That slight resisrance from the knot can cause a backlash or a misplaced pitch -- neither of which I want to happen in a tournament situation!  With my 7'3" pitchin' rod, the leader is probably about 6'6" long, but each rod has a different length from top to reel, so adjust accordingly.

Honestly, I make it as long as I feel like pulling off of the spool

Usually it's 3 to 6 foot long. I have never noticed any difference using either size (or any in between). All the waters I fish are stained, so I'm sure it would matter in gin clear water, but for stained, your lengths would be just fine.