Wear shoes suitable for hiking, with high tops, if possible. This is very important. If your shoes are too loose, wear an extra pair of socks. If your shoes rub anywhere you will have blisters and I can tell you from exerience that a blister out on the trail, away from any help, is torture. Take a small medicine kit (emphasize small) with bandages, just in case.
If you are just starting out, make the backpack as light as possible. Don't overdo it until you are used to the shoes, the physical demands and the load.