My advice after 15 years of backpacking and three different packs:
Keep it simple. Limit accessories and unnecessary straps. More to get tangled, more clips to break, more weight to carry.
My preference is for a pack to have a bottom zip compartment, so the sleeping bag gets stuffed in first thing at the very bottom. Then a simple inner compartment for the rest. I like to keep small loose things, like food packages, fuel canisters, a stove, etc, in the Eagle Creek mesh bags- so that way when I pack, I only have three or four of those bags to put in the central compartment. Simple and easy.
I like to roll up my ground mat and strap it vertically on the back outside of the pack. The pack I use has only three accessory straps that allow me to strap something like this to the outside. This is a secure way to strap on a tent or rolled ground mat, versus strapping horizontally from the bottom- and having something stick out and getting caught on trees and such on a narrow trail.
Um.. a simple, quick access pouch on the top is good for grabbing sunblock and storing food for that day's trail.
Here's a non-pack tip I like. I always filter water because I don't like tablets. But kneeling down over a stream with all those hoses is a pain in the rear, and while you're at the stream bank (or returning to it all the time from camp) you're damaging the streamside vegetation. Try this: cut off the very top of a milk jug. Then you can simply walk over to the stream, jug out a gallon of water, and take it back to camp and filter it there. You save the streamside vegetation and avoid uncomfortably kneeling over the stream. Also this makes it so that you can simply boil untreated water for cooking, versus filtering everything (you obviously don't have to filter boiled water