My usual pack for big trips is a Dana Terraplane that I've had for many years. Pretty simple bag design: sleeping bag compartment, main compartment, two external side pockets, and a lid pocket. The sleeping bag compartment gets a sleeping bag (in its stuff sack), plus whatever I can jam in there, which is usually rain pants, extra socks, maybe a paperback. I try to fill that compartment pretty tightly so things don't sag down into it from above.
In the main compartment, I try to put heavy things low and close to my back. That usually means hardware of some sort: stove and fuel, cookset, climbing gear if it's that sort of trip. Of course, you'll be carrying a pretty large supply of food for a weeklong trip, so the bulk of that should go in at this time, too. After that I try to stuff things in based on when I expect to need them. So spare clothes, gloves, and the like would go in low; a jacket for sudden rain showers or to put on during a break goes near the top. Same for my first-aid kit. I may also put my tent, or part of it, low in the pack.
The sleeping pad straps house their intended quarrya sleeping pad. The tent, if it's in a long stuff sack, may get lashed there as well.
The main piece of advice is to pack stuff as tightly as you can; on a long trip, food will likely take up so much volume that pack space will be at a premium. I fold clothing as neatly as I can so seams and lumps aren't too evident, then "screw" them down into the load. Not only will this make better use of pack space, it tightens the load up so it doesn't shift around.
Anyway, I think you'll get the hang of it pretty quickly. Just pack tightly, and keep the densest stuff fairly low in the pack.