Make sure you have plenty of time. Add a bonus day to enjoy nature.
Prepare your next stage well. Review the weather forecast and plan places for rest breaks.
Pack map and compass and add a map app that supports land surveying maps in offline mode. You can then see your current position and measure distances. Don't forget the power bank and waterproof bag.
Always invest in wool closest to the body. Shell and rainwear protect against rain and wind. Use the "layer-on-layer principle" and bring a hat and gloves.
Low shoes work well on smooth, nice trails with light packing. Boots are best suited for longer hikes on uneven ground and with heavier packs.
Food and drink are important for stamina. Take lots of good breaks and the experience will be better. For day trips, a cold lunch bag works, but if you're going to be out longer, you need a good outdoor kitchen.
Pack as lightly as possible. Tips on packing lists can be found here, on STF's website. It is important that your backpack has a waist belt and chest strap to relieve the burden on the shoulders.