For maximum stability, load your backpack so the heaviest equipment is next to your back and centered in the pack. Medium-weight gear should be carried toward the top and outside portion of the pack and lightweight gear, like your sleeping bag, should be packed in the bottom. A loaded backpack shouldn't exceed 25%-30% of your body weight. This is a general guideline, experienced backpackers might be able to carry slightly more, while beginners might want to start with less weight.
The bottom of your pack is best for bulky gear and items you won't need until you get to camp. Examples include sleeping bag, sleeping pad, any layers such as long underwear you might sleep in, camp shoes, etc. The core of your pack is best for dense, heavy items that you won't need to access during your hike. Item examples include stove, food stash (entrees, not snacks), cooking supplies, tent body, extra clothing. The top zone of your backpack is best for bulky items you might need on the trail. Items that can be put in the top zone include rain jacket, first aid kit, water filter or purifier, etc. Accessory pockets are good for essential items you might need urgently or often - such as a map, compass, sunglasses, lip balm, snacks, headlamp, water bottles, ID and car keys. Tool loops are best for oversized items such as trekking poles, tent poles, crampons, climbing rope...