Welcome to the guide about Jayce, an Ad melee/range. Jayce is a perfect champion for people who like to jungle, solo or just do a heap of damage. This guide will consist of the many needed things that will help you become a wonderful Jayce.

For runes, you would build straight ad, as Jayce has low starting AD, this bonus AD is much needed!
Full runes consist of;
Marks- Tier 3 (Greater Mark of Strength) (+0.95 AD) x9
Seals- Tier 3 (Greater Seal of Strength) (+0.43 AD) x9
Glyphs- Tier 3 (Greater Glyph of Strength) (+0.28 AD) x9
Quintessences- Tier 3 (Greater Quintessence of Strength) (+2.25 AD) x3

This all adds up to be a total of 22 bonus AD
With Dorans Blade as your first item, you would have 85 AD.

For masteries I take 21/9/0
Taking all AD Enhancements in offense.
In defense, I take;
Full Magic Resist
+6 Health per level
+30 Health

This gives Jayce the much needed early game bonus of health and survivability.

I open up with 1 Dorans Blade, when enough gold is obtained, I move into my second Dorans Blade.
I then go straight into boots of speed, then build into either Mercury Treads or Ninja Tabi (I almost always build Mercury Treads if there is even one AP user). I then go straight into Phage as it gives bonus health and attack. Once I have roughly 1900g, I buy both a Sheen and Vampiric Scepter, as this gives the bonus basic damage when changing from both Hammer and Cannon along with the lifesteal. I build into a Trinity Force, with this being one of my main sources of damage. Once the Trinity Force is done, I move straight into a Phantom Dancer, as the movement speed and attack speed greatly help. I buy a B.F Sword and build into a Bloodthirster. Once This is completed, I move into more damage, buying Infinity Edge and then a Black Cleaver. Once the build is complete, I buy all potions, (Ad/Ap/Health/etc)
This build is more of a straight out damage dealer.

When laning in 3v3's or 5v5's, I always take a solo lane, as farming for items is much easier. I tend to harass champions in ranged mode, switching to melee when I feel like adding that extra amount of damage before ending it. In range mode, I poke at the champion, lowering there health until they start to back. I get into range and fire my Acceleration gate (e) then I fire off my shock blast (q). If this hasn't finished them off, I chase while changing into melee for the speed. I jump on them with "To the Skies" (q) then land a "Thundering Blow" (e). This should do the trick into ending most fights.
While wanting to start into a fight, I always go into range and use my e and fire my q through it, making sure it hits the champing. I change into melee and q the champing, (while using q, make sure you use w for the bonus AOE damage) then landing a solid e. I continue to basic attack while changing into ranged for the bonus basic damage and range.

For the people who are new to Jayce, I suggest using Heal and Flash. As this makes it easier to survive and escape quickly.

For the players who feel more confident, I suggest either Ignite and Flash or Exhaust and Flash.

Overall Jayce is a fun champion to play, dealing a heap of damage no matter who you are against.

Credits for my mates telling me to create a guide :3