I know my guide isn't as flashy as everyone's but its still strait to the point and tells you what you need to know, so i hope this helps and you get a lot of good games with Jayce.

For runes you want the magic resist per level and the flat armor, but quints are your own choice, i prefer AD then movement speed but if you need the extra speed go for it.

Masteries are all about the build, if u wanna go tank,bruiser Jayce you might need the increase in defense mastery's but if u want the extra damage, go in offensive, but if u go ADC you need all the damage you can get.

For items if your going ADC and your a little too squishy you might want a warmogs armor or a banches veil for that pesky AP carry. No matter what you should always try to get your trinity force first, with Jayce being able to spam his ability's all day long the sheen proc is amazing, stacking with the added attack on your ult is amazing. For tank you can get almost anything, from warmogs to frozen mallet to thorn mail to Force of nature.

The reason you wanna level Q up before anything else is so you can throw down warp gate and poke people, when the get low you wanna ether chase them down with the cannon or if they are getting a little far away jump to them with Q from hammer stance and melt there face off. After your Q is maxed you wanna level your E for the hammer stance % damage, it;s like being poppy with the added benefit of having range.