What are some good sites or tips for teaching a dog how to heel?

[King of the Castle]

She's about 6 months old, and we've only had her for about a month. Got her from the shelter in February and are now able to walk her since it's a little warmer. Any tips or sites on how to get her to do it would be great. She tugs a lot when she walks, and sniffs everything. Great dog though. Since we've had her, we've taught her to sit, speak, shake, lay down, drop it, and go to your cage. VERY smart dog. She still enjoys using her teeth when she plays too, just not aggressively. Thanks for your answers!