Oh man I love playing Dragon, I love playing it so much (other than the 7/9 characters I have being dragons, and making about 20 different ones) I made an account JUST to give you tons of info and advice on being a dragon!
Oh my where to begin, I guess we can start with advantages and disadvantages, I warn you, dragon is not easy mode, but it is fun to play and is not only rewarding to good players who can use it well, it is rewarding to bear flippy flippy mask of the poop.
On another note, I dislike 'testing' things, most of my information is qualitative (not really number based) I will be telling you these based on my experiences, however I do know most of (if not all) of the numbers as well, I will let you know if I am pulling it out of my butt.
Disadvantages:
You cannot wear armor.
Oh wait, that is the disadvantage, I kept thinking of all the things you can't get because of that...
You cannot:
-Have poise (either its 40 or 0, it would be more logical to wear armor and wear the DWGR instead of using dragonform, although I enjoy wearing the wolf ring sometimes, as dragon, I usually suggest not wearing it. It does help, but not as much as you may expect.
-Have high defense, no matter what you do (with rings etc), your defense will be hard to pass over 200 (the blue tearstone ring would probably break it somewhat easily, but its doubtful it would protect you while its activated).
-Have toxin/poison/bleed resistance. You will be surprised how much it matters. I highly suggest you always use a bloodshield or any 100/100/100 guard shield (against toxin/poison/bleed) You will absolutely need it. Even the impressive 92/92/92 (or 90/90/90) of the Sliver/Black Knight Shield isn't great protection. In this train of thought, I have trouble suggesting using a tower shield other than Artorias's. They (should they have another type of damage, as I've seen often with bleed and katanas) just spam it at you, usually winning quickly. (I will go over more weapons in detail later)
Technically there is only one disadvantage, but trust me, its is huge. there is a reason people hate DWGR (armor is extremely important). There truly is one advantage to get excited about.
Advantages:
Dragon's Breath- This is quite a utility, its effective against slow people (which are extremely uncommon). It NEEDS to be used in short small damage bursts. At level 3 in the covenant (qualitative) it deals ~92 damage a hit to the hollow zombies in burg (not the soldiers). What is special about it, it does deal high poise and blocking-stamina usage damage. If they block it or take it all, they will probably stagger, however, usually to do that, you will need to use your entire stamina bar. The longer you use it, the more stamina it takes. Hence why I suggest short bursts. It is effective on smaller enemies, not so much on players.
Dragon Claws- This are, honestly, quite bad. They make excellent assassin tools. They have an AR of 400 (how do I know? Try BS on an enemy, when you deal damage with your claws, it enhances your AR from 20-400, you can only see this when you hit someone. This is why the dragon bow bs glitch works, it buffs the bow's damage). It also has higher crit. I dunno what it is, but it doesn't usually outdamage (my favorite weapon) a +5Chaos Gargoyle's Halberd with a BS. I wouldn't be surprised if it did with a parry though. Now why do they suck? 400 single damage is quite fair, especially considering they do not require any stats to work, but they moveset (if you can call it that) is, well, just worthless. Smack Smack Smack. Its extremely hard to hit another player with them, and the damage isn't crazy great either. They do look cool though.
Dragon's Roar (get excited! Oh wee oh wee oh wee!)- This is the ability that makes it worth it to be a dragon (other than looking cool, btw, no one remind me that this is like force, but with the disadvantage of having no armor). This roar has more range than force (based on my own thoughts, I use a cleric knight fellow, and after using both, I feel as though roar has more range). It seems like WOTG has more range than force, I wouldn't be surprised if roar and WOTG had the same range. It increases your AR by 1.304348, at level 3, except the claws, which I suspect increase 100% (it increases your fist damage from 20-40). It also stuns them. I have used it a lot, I will give you some important details:
Enemies with greatshields (oh my bane) certain heavy medium shields (Sliver Knight, Black Knight, Sunlight Shield, to name the most common) and no small shields I have ever seen, will block the roar knockback. It will take stamina of theirs, usually 2 roars will break a medium shield guard, but if you roar into a greatshield, do no roar again unless you like to die. Another cool note: any shield 2 handed will stop the roar (do not read this if you ever fight me online muhahaha), once again, taking stamina.
Poise has never given a consistent protection against roar. I have roared players that seem to ignore it, but usually its followed by a lag stab.
Your roar (qualitative) will use up about 95 stamina (you can use it twice with 40 end, and RoFaP on, and then a 3rd time using up that little sliver left, if you don't mind being open to being hit as your stamina returns back).
Roar is your greatest defense, breath is a good utility, and claws suck unless you want to use them in PvE as no requirement weapons or as an assassin.
Now that you have a look into the abilities of dragon we can discuss some other features, we can start with stat allocation.
There are 2 builds I suggest dragon working for. Low HP and high HP. One of them doesn't care that you're not wearing armor, one resists it and gives you some breathing room. My SL 125 dragon has 99 vit, but my level 80 (with 50 vit) is stronger in comparison to the other levels. I suggest either glass cannon or high HP. Playing with moderate HP will not often save you from a BS or a stunlock, the advantage is not usually worth the spend (at least against other players).
I prefer to play 0 magic dragons, I think roar is a sweet 'magic' that makes it tons of fun to play. I suppose the rest of the skills should be spent how you think, but I have one suggestion you may scoff at. I highly suggest you put some points (3-5-8) into resistance. You will be surprised how much armor protects you from poison. This can mean the difference between someone poisoning/toxin you and not. Remember you can't eat a moss when they are on your tail. You have no poise or armor to protect you while you do it. My SL 80 has 18 res, a Gargoyle's Halberd and a potential bloodshield. I haven't been poisoned yet.
Now I will give you advice on weapons.
Since you have no armor, you need to remember that you can't trade hits. A moderate to fast weapon is generally better (the halberds have nice range too). Since it is quite easy for them to own you if you are using slow attacks all the times. Also, do not exceed 25% equip load. The biggest advantage you have is an extra ring slot. Its not easy to break 25% (without a greatshield), but if you do, I suggest you make changes. DWGR is not something you should need with no armor. Since a fast weapon isn't likely to stun someone, make sure if you roar and hit, you fall back or block right away. You must be close for the strike to occur. That is another reason I suggest against greatshields. They weigh so much, and when they come spam attacks at you, being able to parry (or have poise and start trading hits) is really important. Also I do not suggest small shields (if anyone even uses them), or things like the dark hand or parry dagger. You need a solid shield, one with higher stability and good protection.
The rings I like to use, with my non magic chars are usually, Cloranty ring (SP? the stamina regen ring, I shall call it the flower ring), and the RoFaP (which I honestly hope they remove, it makes the game quite a good deal easier). Since your advantages are based on stamina, roar and breath, I want to have that bar be as big as possible and regen as fast as possible. I also usually use a Grass Crest Shield in my R2, since I usually need it to catch people who run away, or I switch to it quickly to recover after an extra roar.
Oh what was I saying? I shouldn't have started thinking of my pvp's as dragon, oh yeah.
I think of this flow chart when I play, I suppose it hinders my ability to play the game, oh well.
Are you or they lagging? If yes than you will probably lose. Poise and defense are really important to fish slapping.
Are they using a greatshield or heavy medium shield? If yes, I consider it a hard match, if no...
Can they fast roll? If no, then usually I just roar and beat them to death, if yes, then...
Can they retaliate quickly? If yes, roar is dangerous and ineffective to use. Roar->roll and counter is a dangerous game to play. If no then usually roar will win eventually.
If they are using a slow weapon, go for BSes. I dislike how people call it fish for BSes. I suppose I do that, I guess if they have a greatshield and a Zwei I should just go toe to toe with them right? You will have to use your speed to hit them when they strike. Many players will underestimate you, and rightly so, its hard to play and many dragons are pathetic cheaters, which brings me to the last point.
Do not dragon machine gun.
Do not dragon machine gun dragon roar (making you nearly invincible).
Do not use the bow BS glitch.
Play legitimately. It may be easy to win with cheating, just like with flippy flippy mask of the poop, but like Dark Souls teaches us, its not about you dying, its about the way the victory feels. Bring honor to dragons roar!
If you have other questions, which I may have forgotten to answer anyway, please feel free to ask, I have tons and tons of experience as a dragon. Which reminds me...
Dragon pyros aren't often effective, the most important pyro, great combust, usually doesn't work against anyone with poise with your no poise. Some pyros are helpful, but I can't suggest a pyro dragon build, as my first dragon was.