If ye want to portray yerself as a bloodthirsty pirate (and let's face it, who doesn't?), ye have to take an affect to yer speech. No need of immersin' yerself in literature, nor takin' any theatrical dialects class. Just remember these five rules:
Any word with an -ing endin' now has an -in' endin'. Most of us do this anyway ("are you comin to the party?"), but with pirate speak, you actually hang on and give emphasis to that final N.
As soon as ye show yer scurvy face-- at home, at the bar, at the underground cockfightin' den, or wherever-- immediately establish your piratocity by greetin' everyone with a hearty "ahoy!" It's how pirates say hello. In Klingon, the hello greetin' basically amounts to "what do you want?" In Pirate, the hello greetin' basically amounts to "I see you."
Yes & No
Simple as mud. This rule alone will make you sound like a pirate. If you forget all the others, remember to say "aye" and "nay" in answer to questions of truth-value. If someone tells you to do somethin', and you decide to do it, say "aye" twice.
To Be or Else
Pirates do not conjugate "to be." I be a pirate. Ye be a scallywag. She be a saucy wench. They be askin' fer a keelhaulin'!
Friends & Enemies
Finally, when addressing friends, call them "hearties" or "maties." Call a disreputable friend a "scallywag." If someone pisses you off, call them a dog. Nowadays, "dog" is what male friends call each other. But in the Golden Age of Piracy, there was nothing worse you could call someone than a dog. Tone of voice helps-- say it with spitting anger. You can add adjectives: "Ye scurvy dog!" "Ye damned dog!" or make it poetic: "Avast, ye bilge-sucking wagtail!"
Right, that last one be a bit complex. But follow some or any of these rules, and ye will be well on yer way to a life of adventure and plunder! May fortune smile on yer voyages!
P.S. There's a new comic coming out in April called Cursed Pirate Girl. We're not sure how much actual piracy is in it, but it sounds mighty interesting and the art is made to look old-timey. Read an interview with the artist and see some pages here.