Hello, I am aidanderson (summoner name and mobafire name) and this is my first guide. I am a level 30 player and my favorite role is ad carry. This is my first guide on mobafire.

Burst:

Jayce has extremely high burst damage with his E->Q combo in cannon form.

Sustain:

Jayce does not have the best sustained damage, but his sustained damage is decent.

Escape:

Jayce can escape extremely well with is ult and his acceleration gate.

Chase:

Again his ult and his acceleration gate help get him chase people.

Health:

He is a dps champion, this is where he lacks.

Difficulty:

Not entirely difficult, but have to his your E->Q combo to nuke squishies like the enemy ad carry and ap carry. Other than that, Jayce isn't that difficult.

Low ELO effectiveness:

Most people won't be smart enough to dodge your skill shots in Low ELO play so you will be able to easily nuke people.

High ELO effectiveness:

People will dodge your skill shots, but with a stun(alistar, tari, leona) then you can easily hit your skill shots.

Pros

High burst
Good escapability
Good chase potential
Good early game
Lots of utility

Cons

Not the best sustained damage
Low range
Falls off late game

Jayce is not a traditional ad carry. Jayce is more of a shut down carry that goes bot. He is similar to Urgot (pre mega nerf) in the fact that he does a high amount of burst damage to squishies forcing them out of lane allowing him to farm easily. He doesn't snow ball as well as most ad carries and he benefits from early victories rather than hour long games with team fights itching to happen.

Ghost:

I picked ghost on Jayce because he benefits from movement speed. His ult gives him 40 movement speed. multiply that by 35% and you get a bonus 54 movement speed. In general ghost just gives more of a sustained chase. You may not be able to ghost over walls like you can with flash, but it gives movement speed for a longer period of time and you can chase longer.

Exhaust:

The debuff on the enemy ad carry is too strong to pass up. 70% attack speed debuff is just extremely strong and can tilt engagements in your favor possibly to get a kill.

I take Summoner's Wrath so that exhaust gives me armor reduction. I get Brute Force for flat ad and Alacrity for bonus attack speed. Weapon Expertise gives much needed armor penetration along with Sunder . Deadliness gives bonus ad per level which is good. Lethality gives crit damage which cant hurt. Vampirism gives some lifesteal. Executioner lets you do more damage to low health targets. I get 3 points in Hardiness because in bot lane you face an enemy ad carry who does physical damage. I get Resistance to get to Durability and more importantly Veteran's Scars . Both of these give much needed hp for survivability in the lane.

Not much to be said here either. These are standard ad carry masteries. A bit of armor penetration, attack damage, armor, and magic resist.

I max Jayce's Shock Blast first for the most burst in cannon form. Some would say max his Thundering Blow next, but this is not good if you are mainly staying in cannon form. I max his Hyper Charge next because it adds to your dps in cannon form. Get your ult when possible of course. Max your Acceleration Gate last for the movement speed buff.

Stack ad over attack speed because your Hyper Charge gives max attack speed for 3 attacks, so you dont need early attack speed. You stack damage so that your Shock Blast does a ton of damage to the enemy squisies.

Start Acceleration Gate, then shoot Shock Blast at the enemy through Acceleration Gate at the enemy ad or ap carry. Follow up with auto attacks and Hyper Charge. Before a team fight be sure to have your passive from your ultimate ready. The armor penetration will make your combo do a lot more damage.

Mainly you are an anti-carry until the carries are dead in a team fight. Nuke their carries and get them out of the fight. This allows your team to clean up what is left and to focus on the second damage dealers: bruisers. You do most of your damage with your spells, but your auto attacks are very strong so don't forget to use them.

Because of his short range, Jayce is not a good vs a caitlyn, tristana, or varus due to their extremely long range. Due to his shorter range, you should constantly harras the enemy. Try to push the enemy out of the lane. If you can do this, you can win your lane. After you push the enemy ad carry out the lane, switch to hammer form to regain mana for when he comes back in lane. In my opinion, Jayce is a different version of Ezreal. They both play similarly to each other. They both have strong skill shots and they have good escapes. Because of this I play Jayce similar to how i play Ezreal: lots of harrasment.
Pro tip: if their support is squishy (soraka, janna, sona, ect.) then you can easily kill them due to the fact that their armor and health tend to be lower than the ad carry. Even if you dont kill them, you can push them out of lane allowing for free farm since the ad carry will play cautious since he cant receive heals.

If you lost your lane, try to take the enemy tower when the enemy ad carry is out of lane. If you kill both enemy heros in your lane, go with your jungler to kill dragon. You may not need your jungler if you have a vampiric scepter or if your support has a heal. In lane still try to harras to get free farm. Something to remember is that in engagements against the enemy ad carry dont be afraid to switch to hammer form. You get armor and you can use the gap closer and the knock-back to get a kill easily. The armor will keep you from dying and the gap closer is a good slow.

Ad carry Jayce doesn't snowball as well as other ad carries in League of Legends like Vayne. But if he can shut down the enemy ad carry, then he will be successful. Most people think Jayce sucks late game as ad carry. This is not necessarily true. Jayce is a good ad carry, but is not a suggested ranked game pick (unless you are in elo hell since it doesn't matter). He is still strong late game, its just he wont do massive true damage like Vayne.

If everyone gets their full item build, Jayce will probably fall off pretty hard since he is better in early game victories when played as adc. If it does get this far into the game, just focus on killing one of the enemy carries in battle and you should do your part.