Okay, it's pretty standard 'play-to-win' knowledge: every good Eldar army has to have at least two Fire Dragons squads, arguably three. Where I differ is the unit size. Current thought is 5 in a Wave Serpent for a 'Suicide-Stop' tactic - but I'm not digging anything for Eldar that includes includes the word 'suicide.' Here's my basic thoughts, without a lot of explanation.
If you're going with 5-man squads, you'd better have 3 units. Waveserpents are a must - Falcons for Dragons is a tactic that's long past. This is the route my buddy Gauthic is going. He's also outfitting his Serpents with Shuriken Cannons; this is the most cost-effective outfitting, given you're going to get close to the enemy for the drop-off.
Fritz advocates, and I believe this to be true, that 6-man Dragon squads are the optimal size. If you don't already know, and if you're reading this I'm sure do, Fritz is the man for Eldar online.
Where I differ is my advocacy for 10-man Fire Dragon Squads, complete with Exarch and Dragon's Breath Flamer. Yes, it's a pricey squad, but consider. People think nothing of maxing out squads of Marines, or Orks, or so-on. Then it gets to Eldar... and cost becomes an issue. I understand. The idea is Wave Serpents are expensive, so to keep up with the mech of other 'dexes, you have to cut your costs. My problem with this is the concepts of durability and utility.
My Dragons - pardon the flash of my camera. The idea of my Altansar is red armor for the Guardians and Black for the Aspects. I broke the 'black' rule for the Dire Avengers, which irritates me when I look at them but I don't want to repaint the squad. Anyway, I painted an orange-helm unit and a yellow-helm unit for my two, maxed out Fire Dragons squad. I was fine with this, but once I stepped back and looked at the army I didn't feel the paint scheme worked. Too many disparate colors. Anyway, I'm repainting all the Dragons, and any future Aspects, with Black armor and red helms. I hope that ties the army together better.
Durability: When the Wave Serpent crashes I want the Dragons to stagger out, ready to kick ass. Okay, their armor isn't great, but 10 Dragons are that much harder to kill than 5. I need them to stay a threat until my opponent kills the unit completely.
Utility: I use my Dragons to target squads as often as tanks. When I shoot something, I need it to die. Completely. All the way. Gone. You get the idea - Melta is great for that. 20 Dragons on the board makes my opponent leery of getting out of his ride. My idea is using Bright Lances from a distance to crack his tank, then swoop in with Dragons to kill off a squad. Even Terminators have something to fear.
Without spending too much time on it, those are my thoughts. Usually I played a 10-strong Harlequins squad as my 3rd Elite, though these days I'd probably add another 10 Dragons.