The "how" to pack any bag usually has two goals:
* packing the bag so it rides well when you're wearing it
* packing the bag so your most commonly used items are easily accessible
There are many resources for loading a pack so it carries well. The main idea is to get the heaviest items you're carrying closest to your center of gravity. You can then put light and bulky items (like a sleeping bag) elsewhere to fill out the pack and help stabilize the load. You can and should always test run your packing plan by loading either your actual equipment, or objects that weight what your equipment weighs, and then going for a nice walk.

(More discussion at:
http://www.wildbackpacker.com/backpacki ... -backpack/)
Note:
A) External and internal frames are packed slightly differently.
B) The "center" of gravity differs for men and women.
C) Terrain considerations are also a reason to deviate a bit from the standard locations.

(More discussion at:
http://www.princeton.edu/~oa/ft/equipme ... ment.shtml)
RonnyRonin's post from a similar thread also has a nice tip: lay the backpack with the frameside on the ground (versus standing the backpack "up" on its bottom) to load it, so the heaviest weight "falls" into the correct place as you're loading things. (
http://www.zombiehunters.org/forum/view ... 5#p2536675)
Figuring out how to pack so that the gear you need is easily accessible is usually fine tuned through trial and error: go on a lot of trips with your gear and see what works and what doesn't. But for initial ideas about where to put things and how to organize them inside a pack, see the following threads:
How do you organize your bug out bag?
Where do I put all those little things into my BOB?
Organizing your BOB?
B.O.B Packing Issue
And finally, review the "Show off your BOB" thread (
http://www.zombiehunters.org/forum/view ... =14&t=4103). A lot of people will show their packed bag (in addition to a complete shot of its contents), and then have photos of where everything is located.