Budgeting backpack weight and making the best use of space are the biggest challenges for a rookie backpacker. Some backpackers become fixated with packing the lightest possible pack and ultimately turn toward ultralight backpacking. But many of us just aren't willing to give up so many comforts, even on the trail.
The best a backpacker can do is carefully consider what to take, choose the options that weigh the least and pack thoughtfully. When you lay out what you plan to put in your backpack, set aside the necessities first -- your sleeping bag and tent, fuel, stove, sleeping pad and the hiking essentials. Then add your food to that pile. Within the space and weight you have remaining, pack your clothes. When you pack your pack, put the small items you'll need throughout the day -- sunscreen, insect repellent, your map -- in the outside pockets. Always return those items to the same spot while you're on the trail, and soon reaching for them there will be second nature. If you still have room in your pack after you've packed all the necessities, and your backpack isn't already too heavy, add any personal items you'd like to bring -- perhaps a book or journal.
When planning your meals for your trip, eat any fresh fruits, bagels or other heavy foods in the first day or two and save your dehydrated meals and noodles for later on in the trip. This will help to lighten your load as you become more fatigued over the course of your trip. Also, learn to accurately read trail maps so that you can determine exactly how far apart water stops are. That way, you won't carry more water than is necessary.
Once your backpack is packed, you can use compression straps to tighten it up. This won't lighten your load, but it will keep it closer to your back, making it easier to carry. Before you head out for your trip, practice carrying the loaded backpack around your house or even through your neighborhood. If you have time, a few of these trial runs with your fully loaded backpack provide an excellent chance for you to decide if you can handle the weight and if the weight has been packed most comfortably. After carrying a backpack that weighs up to one-third of your weight for a few hours, you may be surprised at what you're willing to leave at home.