Playing as brand you should never be stay in team fight. I mean in team fight you just stay behind and stun and spam all of your ability including ult. Brand is squisy but strong, so you want to keep harassing your enemy slowy.

For runes I use megic pen mark, ap per lvl seal, and flat for glyph and quin. This runes allow me to do a lot of damage early and late game.

My mastery is 19-0-11. This mastery allow me to do extra megic damage on enemy.

As I said brand is squisy so you want to get some hp as at start. Doran ring will give you hp and mana regen because we don't have mana regen at all. after doran ring when you have a chance to head to base you want to get at least a boot of speed (350) and you want to get a catalyst the protector that's the best item for brand as he's squisy and no mana regen, Then build it into rod of age. After the sorcerer boots ( megic pen) and rod of age, it really depends on your enemy. death cap is the best item that'll do a lot of damage for the team fight. what you got to do is using your ult.

For the skill q,w and e, max out your w first, then e, then q is the last max out. Note- When there's a single enemy you want to use your e then q to stun, then use your W it will do extra damage. In the team fight you want to use your w then q to stun one of them then use your e it will spread out to all of your enemies around the area.

For the spell I use flash and ingite, flash is the best for mage. If you solo mid, make you u can kill ur enemy, u can flash in and stun ur enemy immediately and ignite and use all of your spell that you sure to kill your enemy. Flash will allow you to esc if your enemy focus you in the team fight then u can just go back and spam all of your ability and win the gank.

ton of damage/mana and squisy.