This guide will give you some solid pointers on how to Ryze to the challenge in middle lane. Be advised that he's not a one-champion-rule-all type champion. He has counter-picks and weaknesses like every other champion. L2Ryze HERE!

Mark of magic penetration [or even hybrid armor/magic if you like using the Muramana/Gaunlet combo on him for split-pushing, extra cc and damage] - will absolutely benefit you since Ryze deals all magic damage, and has ranged auto's.

Armor Seals - are best on Ryze because the majority of games has at least an AD champion. There're also minions and towers, and armor will help reduce damage, and thus keep you alive better while you avoid feeding gold to your enemies.

Magic Resist Glyphs - best against mages and tanks that like using Sunfire Capes.

Movespeed Quints - best choice since AP quints don't benefit Ryze that well, and he can sure use some extra mobility to avoid getting tagged by skill-shots and/or ganks due to being out of position.

Building mana on Ryze is the equivalent of building AP on a mage. Ryze needs damage in order to stay relevant, and the best and almost only way to do this is to build the best mana items on him in order of in-game priorities.

Rod of Ages - Health and mana = HELL YES!
Frozen Heart/Icebourne Gaunlet = Counter AD champs while taking less damage from minions and turrets.
Muramana = Yep! So much mana [damage], and it synergizes well with Icebourne Gaunlet for split-pushing and added cc and aa damage!

Banshee's Veil/Mercury's Treads - Anti-Mage and CC. It also helps reduce tank's Sunfire Cape damage. It also helps prevent being insta-gibbed so easily by one-trick ponies like Warwick and his ultie.

Feel free to experiment with other items like Spirit Visage and/or Will of the Ancients, though. This guide isn't a bible! xP~~

Pre-6, I use:

E->W->move+AA[auto-attack]->Q->move+AA to maximize damage on trades.

Post-6, whenever you need to chase a low target, and/or whenever you need to escape and/or recover health, simply press R, and then do the same thing as prescribed above.

Flash - is the best spell for closing in on last-hit champion kills, or for escaping over walls during sticky situations.

Teleport - It's awesome for quick-returns to mid during early game, assisting other lanes, split-pushing, and even back-dooring!

Barrier/Ignite/Exhaust - They're all very useful, and have purposes. I just don't find myself using them nearly as much as Teleport, though. It's just my personal preference, though. You decide what you want to take.

Any other spells I didn't list here are not of any significant value to me. You can feel free to try other spells out, though.

Learn2Ryze! :D

Pros:
Bursty
Tanky
Late Game

Cons:
No built-in gap-closers or escapes
Outclassed by some mages
Early Game

Have your jungler gank for you, and follow up with him smartly.
Teleport to other lanes when your allies are in need.
Try staying in groups of two or more while wandering in the jungle, especially if not warded properly.
Always target squishy enemies first, like the AD and/or AP carry.
Give your best!

Use Q to last-hit cannon minions, and even melee minions, if you're bad at last-hitting.
If you get good at last-hitting, then this means you can spam Q less on minions, and more on enemy champions = HARASS = GOOD! :)
Always get three to five health potions if you plan on killing the blue golem and/or some jungle monsters, though the best thing you can do is defend, freeze a lane, and/or farm a lane.