Use Overload's passive to optimize for maximum damage or maximum survivability.
Spell Flux's short cooldown allows it to be used to spread Flux to many enemies.
Ryze can move and cast other spells while Realm Warp is charging without cancelling the portal.
Playing Against Ryze
Ryze is especially dangerous to opponents that are marked with Flux.
Use Realm Warp's windup time to figure out how to deal with what may be coming out of the portal.
Crowd controlling Ryze during Realm Warp's windup will cancel the portal.
Even though Rune Prison is commonly maxed last due to it's root duration not scaling with ranks, it's a decent choice for a level 1 pick, since Overload and Spell Flux do little by themselves and early game mana doesn't allow for very many combos; addittionally Overload can be blocked by enemy minions, making it hard to land on champions during laning. Rune Prison can be used to halt the enemy if they attempt to burst you early.
You can cast an extra Overload between the Spell Flux and the Rune Prison for extra damage, but be aware that doing this will not trigger the shield as Runes will be consumed every time Overload is cast. Since Rune Prison has a long cooldown and you will be left with just Spell Flux to charge Runes, make sure to make the right decision between gaining the shield or the extra damage.
Overload can be used with relative freedom once enough bonus mana has been built, since it's cooldown is refreshed by your other spells should a fight break out. With just a couple of items and a few ranks, it does a decent chunk of damage even without combos to enemies who don't dodge it in time.
Ryze's full damage combo is Q > E > Q > W > Q > E > Q
This full combo only works with near max CDR due to your E being cast twice. This is the main combo that you'll be using most of the time.
Ryze is one of the best users of Phase Rush due to his natural 3-part combo, which also stacks with the extra movement speed gained from Overload's shield; allowing him to easily both catch up or run away as the situation requires.
Arcane Comet is also good on Ryze; just a Rune Prison even without Spell Flux is enough to guarantee a hit for a nice amount of poke in the early game, and it also cools down quickly as all of Ryze's abilities are single-targeted.
Electrocute is also triggered by Ryze's natural combo, useful if you desire more burst damage.
Ravenous Hunter is an useful pick as Ryze has no healing sources, and all of his abilities are single-targeted, giving him full benefit.
Relentless Hunter is a good alternative if you like to roam more, and later in the game it allows you to reach the fray faster.
Ryze's abilities scale with both Mana and Ability Power, which makes items that have both stats much more effective for increasing his damage output.
Arcane Mastery gives Ryze bonus Mana based on his Ability Power. This makes Tear of the Goddess an essential item early game, since spamming abilities gives you bonus mana, due to its passive effect. It should eventually be upgraded into Archangel's Staff as your second item.
Rod of Ages is commonly the first finished item as it gives Ryze everything he needs; ability power, health and healing, and mana as well as mana efficiency, all of which synergize with his abilities and make him more durable.
Ionian Boots of Lucidity are the most common boots choice on Ryze, as more cooldown reduction equals more Spell Fluxes, which are the basis for Ryze's damage Sorcerer's Shoes are also a valid choice for dishing out even more damage, if cooldown reduction is compensated from runes or other items.
Zhonya's Hourglass is a good situational item on Ryze, useful if going against an AD-heavy team or assassin champions. Note that the tactic of putting yourself in Stasis to guarantee a successful Realm Warp is no longer possible; activating Zhonya's Hourglass while channeling will put the ability on cooldown.