RUINS (do not purchase ruins at low levels (lesser ruins):
Recommended Priority order - attack speed, ability cool down, ability power, attack damage, armor, magic resist, health

Purchasing Items:
Always buy the attack speed items first!!!!
1st - Berserker Grieves (I recommend purchasing dagger first)
2nd - Nashor's Tooth
3rd - The Black Cleaver
4th - Phantom Dancer
5th - Force of Nature (1st buy Negatron Cloak. Then buy Regrowth Pendant, sell your Berseker Grieves and buy other Regrowth Pendant)
7th item - Thornmail
8th - Boots of swiftness

Don't be concerned at low defense at start of match:
You're thinking you'll have low defense, but with attack speed high, turtle shell active and phoenix flaming in rapid burst, enemies will be quickly killed before they can deal any damage to you. This is true to everybody except Tryndamere when his ultimate is active, this is the only time its possible for you to die in a 1v1. When other enemy champions come to assist the mid you're owning. This is when your summoner spells come in handy :D (retreat to your turret, which should have full health, quickly).

Attack Strategy:
Spam phoenix (press R each time it becomes available while fighting minions. Get turtle at level 2. Constantly switch between phoenix and turtle; this will keep Monkey's agility (passive attack speed ability 10%) active and at 3 stacks (30% bonus attack speed) in between phoenix cool downs.
You will most likely be fighting a ranged/mage character at mid. Doesn't matter if it's Ashe, Caitlynn, Morgana, Kayle or Sivir. Be aware of their presence, but focus all your attacks on the minions. You should only lose 1 or 2 minions by the time you've killed all enemy mid lane minions. Recall if you need more mana, might have to do this about 3 or 4 times until you upgrade forms as you level (reduced mana cost for each point in ability).

(Optional) This is where 1 point in Bear 3 and 1 point in Tiger at early levels could be beneficial. Bear will allow you to run down enemy champion and "root" him/her in place while Tiger will let you stun them and deal significant magic/attack damage. Then of course you can switch to phoenix (back to regular strategy) and own them. I know switching between Phoenix and Tiger is very tempting, but turtle's shell is necessary until you get Force of Nature and Thornmail.

You'll rapidly earn gold by continually pushing minions to turret and maybe getting a few champ kills, so keep an eye on gold and be sure to recall to make purchases. (can totally forget about buying items when destroying your enemies).

GOOD LUCK TO ALL UDYR USERS! Honestly, you won't need it, you're going to own :D