Loading your pack is not as exciting as starting up the trail, but the success of the backpack trip often hinges on it. Take enough gear and food that you are safe.
The part of a backpack trip that I enjoy the least is the preparation, specifically the gathering together of food and gear and loading it into your backpack. Doing this right is critical though. You want to have enough with you that you are safe and comfortable and well fed, but you don't want to take so much that your pack is too heavy. An overweight pack can make what would have been a good backpack trip become one that is borderline miserable.
What works for me is to keep all my gear together in one section of the house. That makes it less likely I will forget something important. Before I did this, I once forgot the center pole of my tent, because I had placed it in a closet. I was only twenty miles away when I realized this, and drove back to get it. Another time I left without my titanium cooking pans, which were still in the dishwasher. I discovered this 200 miles from home, and so went to a fishing store and bought some stainless steel pans.
A list of needed items is a great way to avoid forgetting something. REI has a checklist for overnight backpacking, to help you get started.
Go over the list as you are loading your pack, and then another time just before you leave.
One of the common mistakes beginning backpackers make is to bring too much along. I do want to emphasize how important it is to keep your pack as light as you can, but still have enough essential food and gear with you. My article about early season backpacking emphasizes just how important it is to bring along seasonal-appropriate gear - in this case, trekking poles.
Knowing just what to bring is a balancing act, and you get better with experience.