Base:
Start with a Sapphire Crystal, this will allow you to harass with your q for a long while.
First trip back buy Boots of Speed and Tear of the Goddess.
Use E and run back to your lane, next farm enough for Sheen and a boots upgrade. ( Heavy AD = Ninja Tabi, ULTRA HEAVY disables = Mercury Threads, otherwise make Ionian Boots of Lucidity or Boots of Swiftness ). If you want you can also wait untill you got enough for manamune, this one will boost your damage by ALOT.


Midgame:
Collect enough for Avarice Blade and Sword of the Occult, these 2 damage will boost your damage output by alot, enough to secure your Sword of the Occult stacks. Next up is Infinity Edge, when this baby is ready, you can deal 50%+ damage with one crit from your Q.


Endgame:
Normaly it won't get this far, people will surrender much earlier when they notice their hp disappear instantly. But if you got a ultra ******ed team, 4 feeders and a huge disadvantage, finish your Trinity Force and then sell Avaruce Blade and buy a Frozen Mallet, no more running once Frozen Mallet is done!


Optional:
If you don't like Sword of the Occult, get The Black Cleaver or The Last Whisper instead.
You can also sell Avarice Blade earlier to get one of these 2 items ( The Last Whisper if 3+ enemies have 100+ armor, otherwise The Black Cleaver.

You might also like some lifesteal early on, get a Executioner's Calling instead of the Avarice Blade. This is especially usefull when you get harassed alot in your lane.

Q: Use this to harass your enemy or get lasthits, this shield never be on cd ( use on mob or on enemy ) In teamfights stay at range and spam this skill, when enemy starts running get in close and finish them with auto attack + Q.

W: Heal yourself whenever no enemy is near, if a teamfight is approaching, save it to get out of a stun ( like ashe ulti, sion stun, taric stun, malz ulti, lux snare etc ).

E: Great skill, will help alot when hitting towers, in teamfights and even while harassing ( extra movement speed allows you to get in range to use Q.

R: This skill has 2 main uses, slowing enemies and finish low hp enemies. Nothing else ( don't use on minions, last hits won't count, don't use to killsteal, it won't give you the kill.

Gangplank is great in mid, but its better in a duo lane with another harasser like Gragas, Katarina, any ranged AD, lux etc.

Use your Q to harass the weakest enemy, if playing against a taric or only focus on one enemy, ( because they heal 2 at the same time ).