Re: Raising a Miltank
The key to Miltank is knowing exactly what you want from her. Are you wanting your Miltank to be purely defence/cleric based, or more of an attacker? She's known as a bit of a tank (and rightly so), but she has a good base speed and decent attack.
Lax isn't the best nature, because even though her Sp. Defence is no where near as good as her defence, she can still take Sp. Attacks quite well with a small EV investment - Lax hinders her ability to do so and will do her no favours. Impish is a much better nature, as it lowers Sp. Attack which Miltank certainly has no use for anyway. Thick Fat is worth a mention too on a Defensive set, as it will halve damage from Fire and Ice attacks. However, you'll be walled by Ghosts to some extent.
Your current two attacks are walled by Steels such as Skarmory and Levitating Bronzong, as well as bulky waters like Swampert for the most part. Gyarados, especially a Dragon Dancing one, will take the opportunity to set up on you.
My Miltank's moveset looks like this:
Body Slam
Milk Drink
Heal Bell
Stealth Rock
She's really great at supporting the rest of my team with Heal Bell, as well as taking physical hits. Stealth Rock supports my attackers and Body Slam has a nice added effect of possibly inflicting paralysis, which helps them again. If you're going for an attacking Miltank, then Zen Headbutt, Hammer Arm and the Elemental Punches may well be worth a look, although I feel that Miltank shines best as a tank. Your moveset is okay as far as defence goes, but your nature could be better. Finally, Curse is another option on miltank. If you get the chance to set up a couple of those then Miltank will be a force to be reckoned with.