Difficulty: Moderately Easy
Step1
Your first option is to stand in line at your nearest Apple store like every one else.
Step2
Your second option is to visit AT&T's website and start service with them as they will be selling the Apple 3G iPhone beginning on July 11.
Step3
Finally, your best option is to set up a "personal shopper" appointment on the Apple website. You can do this up to 14 days in advance of the release--so beginning approximately June 27, those appointments should come available. If you set up this appointment, you may be able to avoid lines (assuming there are lines) all together. To do this, simply visit Mac.com.
Photo from Fortune.com (Philip Elmer DeWitt's Apple 2.0 Blog)