There are several ways to learn forms, all of them require a Player Teacher who has them.
Easiest method to obtain forms is to seek out recruiters for a guild with the desired form as their main. Now its HIGHLY looked down on to do ANYTHING for ooc reasons, but if you go about it in a perfectly acceptable IC style, you'll find yourself quickly embraced. Once guilded in a combat guild (Whitecloaks, Army of the Hawk, White Tower, and Borderguard are your best bets), you'll find willing teachers ready to stuff you fat full of skills and forms. (Also note that PERC plays a very important role in learning forms/skills)
Now, another method, would be to ICly discover combatants who aren't guilded, and ask to be their apprentice. Not the easiest way to gain forms, especially since those that aren't guilded, likely are that way so that either they don't have ties, or so they didn't have to teach to begin with. This isn't to say that it isn't possible, just not very likely unless you happen to be lucky or the person in particular is in a good mood. Best to make friends, and later on ask for favors.
And yet another method would be to hire someone to teach you. You'd be surprised at the generosity that spills from people once they realize payment is involved, but the prices can get fairly steep, so try and keep up a decent cash flow, and seek out those that might be willing to teach you.
The summary of all this would be, RP. You are required to rp, and rp at least decent in order to grab the attention of people. The better you roleplay, and the more IC friends and connections that you obtain, the higher the probability of earning forms and skills. So get out there, and do what needs to be done.
You will also wish to purchase practice weapons for the purposes of doing the least amount of damage when learning forms. All practice weapons -with the sole exception of Ashandarei- are sold in Damodred Manor. You will have to ENTER Damodred Manor in order to find the person who sells it. Although it appears as though the gate guard stops you, there is a way to ENTER Damodred Manor. (If that isn't a big enough hint...)
There is also a hermit mob that drops "a curious wooden pole, with a thin, curving board of wood lashed to one end" which functions as an Ashandarei. I have no hints to post at this time. :-P
Note on teaching forms: although it is a good idea for the person who is learning forms to use the Training Stance, it is actually easier to teach specific forms by cycling through Defensive, Neutral, and Aggressive stances. Each stance pops a certain form more than the others. Or you can start out with training stance yourself, and then teach them about 6 forms or so, and then cycle through for the last 3 forms.
When formtraining you can train in one of three ways
Option 3 is the easiest. Option 1 and 2 allows you to 'minimize' the time it takes to learn a form by having you use less stamina [and hence, less need to regen afterwards]. Fleeing costs xp, but no stamina loss (As of a recent update to promote more RP and prolonged spars, fleeing also resets your RPC to 0). Pick something and go with it.