Shorter is better. Lengthen only as necessary if fish are spooking from your fly line. Less knots are better and pick up less debris, move the weeds less, hang on the weeds less, etc--Use a commercially tapered leader looped to your fly line as your base leader as it will last a long time. Make that a 7.5 leader tapered down to about 4 lb test for Bluegills or 6-10 lb test for bass. Add tippet as needed using a small loops. Coat those knots with Knot Sense to smooth them out and lacking that use Sally Hansen's Hard as Nails and clip tag ends very short.
When making a tapered leader try to match the flex of your fly line with the butt, or go a bit limper rather than too stiff. Drop the diameter of that first section of mono to about 2/3 the butt diameter of your fly line. I leave a 6-8 inch section of soft mono (Amnesia) attached to my fly line with a nail knot ending in a small perfection loop. Then I can change from a Bluegill to a Bass leader quickly. Here's a link that says a lot: TOM JINDRA, Guy Tillotson's Grand Slam Group LLC: Building A Better Leader
and does so simply in an easy to understand manner.