As a Mithran Drg what you're really after is Str. Dex and Acc isn't your top priority... that's for ALL the other races. I solo'd 1-20 cuz I didn't want to deal with the hassle of Dunes (Drg/Whm FTW!). I even went 1-50 with gimp gear and still did better than all the other classes at that point on Acc and Dmg.
For soloing /Brd isn't the best choice by far. Yes you don't need to rest but at the lvl he was you don't get healed for a whole lot, can't take any bad status ailments off of you, and you can't heal yourself in a dire situation like say when your Dragon (yes Dragon... SE can't translate from their own workers) dies. /Whm is quite possibly the best choice for those main reasons... and for those you can stay alive. Pre lvl60 your heal limit is at 33% HP meaning anything under that casting a spell will give you a healing breath from your Dragon. Post60 it gets even better considering you have your Drachen Armet equipped since it starts at 50% HP. At 67 I don't have much Dragon HP%+ equip on and it heals for 210 minimum... that's more than enough to keep a lvl75 Pld alive for just a measly 8MP a pop... if you do the math for how much a Cure4 is... we can heal about as many times as they can. Going /mage in parties I wouldn't recommend but the stats don't suffer much except for Acc.
As far as subs go for lvl's here it is:
1-10: /War for the extra HP, Def, and attack for the simple reason... you have no MP
10-20: /Whm for keeping YOURSELF alive in parties... no one else can be expected to do that. As for the lack of Provoke to tank... no one really cares about it, if anything you can solo like I did... not as hard as it seems killing T bats in MoS near Windy (just watch the 3-set bats).
20-30: /Whm or /War Your choice for what you want to do.
30-60: Here's where it really opens up. You can go from /Whm, /War, /Thf, /Drk, /Blu, or even /Mnk. Reason being is that all those classes get extra abilities or spells to do more dmg or keep yourself alive or taking dmg.
60-75: Here is where the infamous /Sam comes into play (what I use). With /Sam you get Meditate and become what's known as a "TP-whore".
Stacking up on "Store TP+" gear adds to the amount of TP you gain per hit. If you play it right you can get in up to 3 WS's per fight (and when you get Wheeling Thrust you can pull Light Skillchains out of your bum). Seigan+Third Eye can let you tank for a few hits for when you DO pull hate (me personally I tank it as much as I can to make the people actually work for their XP and to get extra skill ups), Super Jump can save you from being killed if you get too low. But the other subs are still good as well if you don't want to be a "TP-whore".
For equipment as I said you want Str.
Head: Anything that gives Str or Attk... if you can't get that you're next best option is the Empress (or Emporer) hairpin. At lvl43 try to get a Valkyrie's Mask, but once you get your Drachen Armet that'll be your headpiece of choice till your late 70's.
Body: Again anything that gives Str, but it doesn't really matter till you get to lvl55 and get your Jaridah's Peti which you can use in parties till your late 70's. Do not... I repeat DO NOT BUY a Scorpion Harness (any race) it's not needed for Drg and is a waste of money. Not saying that if someone gives it to you not to take/use it, but do not buy it yourself.
Hands: This is mainly the only place where Acc can take presidance on on armor... so either Battle Gloves or your Drachen F.Gauntlets in this spot.
Pants: This slot doesn't really matter... if you can get a Garrison Hose or Bastokian/Republican subs that's great, don't want to quest/craft it then just get something for Agi or Dex for this spot.
Boots: Here if you can get the Leaping Boots or it significant other perfect! You can use those all the way to your RSE feet and those can go a long... long... long... way. I still use them at 67 in my parties.
Back: Doesn't matter unless you want to use Traveler's mantle for the extra evasion till you get your Amemet Mantle at 61, that's good till even 75 unless you want to use a Forager's Mantle at 71 or Cerberus Mantle at 75.
Waist: Here you can use a Warrior's belt (or +1) till you can get your Life Belt at 48. From there try and get your Potent belt at 60, which is good till 75.
Ranged: Fishing pole... or at 70 get a Trollbane from the same guy you get Sanction from in Whitegate.
Ammo: Lure? At 50 you can try to get a Kakanpu or Optical Needle from the BCNM or also a Tiphia Sting from the HNM bee in Crawler's Nest. At 60 and 61 you can use a Bibiki Shell (me) or Wyvern Feed. But at 75 get the Angon if you're getting the Angon ability.
Earrings: At 21 get Beetle Earring+1 (x2). Never hurts to have a Reraise earring on the offside chance your party gets wiped or you do while soloing. Use the Beetle+1 till you can get Fang or Spike Earrings at lvl55... after that you can get Assault (lvl58) or Merman's Earrings at lvl63. If you're Drg/Sam try to get a Brutal Earring at lvl75 if you can.
Rings: At lvl14 you should get at least 2 a Courage rings if not the +1 versions and hold onto them till about 36 for you Garnet or Puissance Rings or hold onto the Courage rings till about 50 for your Garrulous Ring or at 54 for your Victory Ring. At 72 you can pick up a couple of Triumph Rings or at 74 you can get the Vulcan's Rings.
Neck: lvl7 quest for the Wing Pendant. lvl21 get a Spike Necklace (Tiger Sole if you plan on soloing any as well). At lvl33 if you can get a Peacock Charm... I hate you.

Weapon: Use anything that's Drg only till you can get the next Lance that's Drg only... using another but the Drg only lance once you can start using them will gimp your dmg. At lvl60 you can use either the GKL (Grand Knights Lance) for the +7 Acc or use the Dark Mezraq for the Eva down effect (for mob) which procs often so the whole party can hit the mob easier and it also does slashing dmg so you can use it on bones.
Remember to try to get the +1 version if you can AND if it's within a reasonable price range of the stat difference on the items.
Final notes...
It's not you job to dumb your dmg down just to keep hate on the tank, you're suppose to kill the mob as fast as you can. Yes you will get crappy tanks (mostly Nin's) which you'll steal hate right off the bat, it's not your fault. I even stopped using food so I don't steal it as fast once I hit lvl50.
As a Mithra NEVER EVER use sushi... another thing that's a waste of money, you can stick to Mithkabobs all the way to 75.
With the 20min timer there's no need to ever dismiss it... now that it's not the 2HR now it'll recharge really fast now.
As for parties it varies per person I guess... I get invites rather quick when I'm seeking and pretty often when I'm not seeking and not /anon.
When you're leveling after 50 in KRT fighting bats you have a GREAT chance to pop off Double Thrust for 900+ dmg so be careful and make sure super jump is ready before you throw that out there... the tank wont be able to take hate back when that goes off.
Umm... if there's something I missed or questions you need answering just put them out here. I'll answer them when I get back on here. /goodbye