For summoner spells you NEED ignite and ghost or flash. Once you get someone to 20% and use ignite along with your ultimate they will die. For runes you want cooldown reduction along with magic resist or health.
The items you get first really depend on the team you are facing. If they are casters you want to get Force of Nature right after boots, if there are a lot of melee you get Randuin's Omen and stack sunfires. But it should generally look like this:

8 Armor, 120 Health, 8 Health Per 5 Sec.
Item Costs: 435

Click: Restores 200 Health over 20 seconds.
Item Costs: 35

20 Magic Penetration. UNIQUE Passive: Enhanced Movement 2
Item Costs: 1100

45 Armor, 450 Health. Passive: Deals 40 Magic Damage a second to nearby enemies.
Item Costs: 2510

40 Health Per 5 Sec, 76 Magic Resist, 8 Movement Speed. UNIQUE Passive: Restores 0.35% of your champion's health every second.
Item Costs: 2190

25 Attack Speed, 20 Attack Damage, 30 Ability Power, 12 Critical Strike Chance, 300 Health, 300 Mana, 12 Movement Speed. UNIQUE Passive: 25% chance on hit to slow the target by 35% for 2.5 seconds; on cast, increases your base Attack Damage by 130% for one attack.
Item Costs: 1525

45 Armor, 450 Health. Passive: Deals 40 Magic Damage a second to nearby enemies.
And then of course throw a Warmog's Armor whereever you feel you need the extra health.
For spells you want to max out Siphon of Destruction and then Creeping Death. You should get one rank of Mace of Spades at level 2.