This is my very first guide. In fact, I created an account just to share what I've learned about Jayce since, as of this guide's post date, I haven't found a Jayce guide I'd invest in. I ask that you read the entire guide should you wish to leave a comment or before downvoting this guide. I will update, append, and add on to this guide as it is needed. I have no clue about BBCode, but will follow any and all suggestions for its use. Enjoy dominating your opponents with this guide.

Pros

+Versatile Toolkit
+Amazingly Fast
+Melee or Ranged at the Press of a Button
+Epic Harass
+Ult at lvl 1

Cons

-Squishy Early Game
-Focused in Team Fights
-Steep Learning Curve to Master Chaining Moves

The runes provided are pretty self-explainitory. Jayce is an AD carry/bruiser. You want to have a good mix of damage output and survivability. Instead of taking 4 straight armor glyphs and 5 armor per level glyphs, you can choose to go all of one kind. You can also use ArP Quints.

The masteries are also pretty straightforward. One could swap a point from Summoner's Insight and place it in Hardiness .

x3
It is always a good idea to start out with Boots and some health pots. This is especially true for Jayce to position yourself for early game harassment via your Q.
x2 or
When you first recall, it's a good idea to either buy two Doran's Blade or start on your Phage. Decide which you want to do based on how you are doing in lane. If you are having a rough time, Doran's Blade x2 is what you want. If you're the dominant player, Phage it is.
or
Building Phage early is essential to keeping your enemies in range for you to attack them. Purchase a B. F. Sword to keep your damage up and remain a threat to your enemies. I like to get Zeal as soon as I have the gold for it, but Sheen is just as nice and is situationally better before making the Trinity Force.
or or
After compleating Trinity Force, finish your boots. If the team is AP heavy, get Mercury's Treads. If they are AD heavy, get Ninja Tabi. If it's an even mix, get your Berserker's Greaves.

Madred's Bloodrazor is an excellent item and does some serious damage with your later Attack Speed. I like to pick up the Recurve Bow as the first item in my Bloodrazor. Once your Bloodrazor is finished, Build Black Cleaver. This item is exceptional for Jayce, because you hit harder and faster. Finish your build with a Bloodthirster and a situational item.
Before the situational item, you should be hitting very hard and quickly. I see crits between 700-900 on auto attacks.
Some great situational items are:
Phantom Dancer- This is an exceptional item. Attack Speed, Movement Speed, and Crit all in one package. I pick this up a good bit.
Infinity Edge- I would get this after Madred's Bloodrazor were I to get it.
Youmuu's Ghostblade- If you need some Cooldown Reduction and a bit more offence, this is it.
Frozen Heart- If you need Cooldown Reduction and some defense, look no further.
Maw of Malmortius and Atma's Impaler are both great situational items based on if the team is AP or AD heavy, respectively.

Maxing Q then W and then E has proven to be most effective for me. Q is a great taunt and gap closer. W is great for farm phase and also gives a slight edge in 1v1 and team fights. E is your power move. When using the Merc Cannon, it makes your Q hit like a truck. While using the Merc Hammer, it makes you hit like a truck and is also great for hitting enemies out of position/interrupting casted ults, and things of that nature. I max E last, though, because Rank one of it is sufficient to finish champions early on. When you are maxing this, most team fights are going on and the increased levels help greatly.

Probable Matchups:

Mundo is a formidable champion, but he's no match for Jayce! Stay behind your minions to avoid Infected Bonesaw and be sure to taunt him with your Shock Blast as much as your mana allows. He looks big and scary, but if you keep him suppressed early game, he'll be a good punching bag for the entire game.

That's right. If you follow this guide, you'll beat the tar out of other Jayce players. He's probably just as fast as you are, so make sure you maintain good positioning. Taunt him with Shock Blast as much as you want. He'll eventually get mad and start doing foolish things. That's when you pounce with To The Skies!.

His mushrooms are no fun, but neither is eating your hammer. Stay at a distance until your To The Skies! and Thundering Blow combo can finish him. He drops faster than a dress on prom night.

Play smart. You can beat him if you keep your distance until the critical moment. Keep in mind that his ult is very powerful. At low health, it's best to try to finish him at range or get out of there.

Draven is no match for you. Thundering Blow him away from his axes and he'll be running from you in no time. This is a great time to swap to range and finish him with an Accelerator + Shock Blast combo.

He's very easy to play against early game. Late game he will usually be able to beat you unless you catch him with a few ranged shots before he gets close enough to attack. Know when to run and when to fight it out.

This was the evolution of the build(bottom to top). As I started coming closer to the current build, the better I did. As you can see in the top game, we lost a 4v5, but the build did phenomenally. It is worth noting that in three of the games shown, there was an AFK/Leaver(one game had a 3v5)- a growing problem in the community. I say this to illustrate that despite overwhelming odds, one can do quite well as Jayce.



A friend tried my build and sent me this picture. this was his third time playing Jayce.

Be gentle. This was my first guide. I expect this to be much better once I get some input from people about BBCode as well as suggestions. Thanks for reading and for all input.