Gangplank is a nice damage dealer depending on Parrrly and some crit chance! he is very good after the trinity Force but before that he can only harras a bit :)

Pros:

His ulti is sweet!
His Parrrly deals tons of DMG!
He is a good minion killer with Tiamat!
He is not that squishy!

Cons:

He dont deal that much damage early-game
you think you can't be killed after u have owned them! (but you can if they are 3v1!!)
his ulti is difficult to hit with!

I think that was it. :)

Parrrly is your way to deal DMG so go up in that as fast as quickly is a good idea..
Remove scurvy is a good idea to level fast too cuz u need that to be in lane and to remove stun and stuff like that.
Raise Morale is good in team fights to make them run faster but its not as important as the other spells.
of course u should level your ulti when u can...!

Its always good to jungle (of course not when there's a teamfight) so u can get ur items as fast as possible! red and blue buff are some good buffs to get for Gangplank so try to get them quick!...