This is my first guide, and not the best really.
Please read the full guide before voting or commenting on it.

Brand is a very strong champion in game and in teamfights as well.

Pros

-Has four strong nukes.
-Can easily deal massive damage to large groups.
-Great in teamfights.

Cons

-Uses lots of mana.
-Often gets focused.
-Slightly difficult to learn.
-Quite Squishy.

This is all your own personal preference, I like getting the early AP for easy harass.
Though, you can do whatever you like.

Marks; Magic Penetration
Seals; Mana Regen
Glyphs; Ability Power
Quintessence; Ability Power

So, lets talk about your items.

Core Items:

-Dorans Ring - Great for AP Casters early, nuff said.
-Sorcerers Shoes - Nice magic pen.
-Rabadons Deathcap - This is the item ALL AP casters should get, should I say more?
-Rylais Crystal Scepter - Lots of HP and AP, and slowing will help you hit your pillar of flame and sear.

Situational:

-Abbysal Scepter - Balance of AP and MR, nice if the other team has a strong AP Carry.
-Void Staff - With this + sorc shoes and runes. MR won't be a problem...
-Deathfire Grasp - Kage's Lucky Pick is a nice GP/10 item, and deathfire is nice against tanks.
-Will Of The Ancients - If you know how to play Brand well, definitely WOTA will be great.
-Mejai's Soulstealer - Playing against noobs or co-op vs ai, go ahead! Or if you're really confident.
-Rod Of Ages - Get this early, personally i don't get this, but nice HP and MP.
-Archangel's Staff - Lots of MP and a nice AP Boost.

Defensive:

-Banshee's Veil - Lots of MR and hp and mp. Also, with that shield and people focusing you, great for Brand.
-Frozen Heart - Lots of armor and slows the enemy team a lot, great to help out your team and a good defensive item.
-Gaurdian Angel - Brand is there to burst them down as much as possible, reviving to do another combo can probably nuke them down to death, or below half.
-Thornmail - GREAT AGAINST AD CARRIES.

Items I usually get;

-Sorcerers Shoes
-Dorans Ring
-Rabadons Deathcap
-Rylai's Crystal Scepter
-Will Of The Ancients
-Gaurdian Angel

Going to the middle lane as Brand can be hard sometimes, depending on the other champion.
Here are some champions that might just f**k you over.

Ahri; Very hard champion to lane against once he hits 6, and if he knows how to play her well. Shes a skillshot heavy champion, so stay behind minions so her charm wont hit you, and move around so that her orb of deception won't get you. I hate laning against Ahri.

Cassiopeia; EXTREMELY hard to lane against, she can pretty much destroy almost any AP champion in mid. Play defensively, because if you try to jump in at her, she will obliterate you with her array of poisons.

Leblanc; Also a very hard champion to lane against, she has that stupid distortion spell which she can use to dodge most of your pillar of flames, and distortion in, sigil of silence, then distortion out. Always try to stun her when she does that, so that she will be the one taking more damage. Do not try to dive her as her Mirror Image will just f**k you over real hard.

Malazahar; Frustrating to lane against as he has a good aoe silence and can farm minions really quickly with Malefic Visions. Though if he gets to low mp, don't be afraid to jump at him as he doesn't have many escaping skills. Once he gets to 6 though, he will just null zone, silence, and ult you and you're dead, if not, he pops down malefic visions and ignite. Sad Brand.