1. Pack light!!!! Take what you think you will need and use. It's counter-productive to bring 'everything'. Highly unlikely you will use it or want to carry it. Bring comfortable, appropriate, warm clothing. Should include a hat, coat, sun glasses, and sturdy shoes. Protect your head, especially the eyes, and your feet. Dress in layers, and take things off if you become hot.
2. A good camera, writing implement, and plain notebook are essential. Don't forget the charger or batteries. Workbook, if you have one.
3. Study what you plan on seeing and/or want to see. Have a plan; don't just aimlessly wander.
4. GPS and APPS for your phone are a great help both before and during your trip.