My hot topic: adequate footwear.
Actually, a novel doesn't need to be written about this - neither flip-flops nor fashionable sneakers without proper support belong on mountain-hiking feet. What you prefer is up to you - it doesn't always have to be a high mountain hiking shoe. Just be aware of your weak points and hiking routes. If you tend to sprain your ankle quickly, a low shoe (trekking or trail running shoe) is not recommended. If you are in rocky terrain, it is also better to choose a high hiking shoe because of the unevenness and the risk of injury from the stones, or when crossing streams. Don't forget good, non-slippy soles - remember that it doesn't have to rain to be slippery - the ground is often damp in the morning, even in the shade until later in the day. Vibram soles have proven themselves here. A rather coarse profile is also advantageous.
And no, it is not enough to have worn brand-new hiking shoes (no matter how expensive the brand is) during office hours the day before. You do your feet and joints a favor if you have been wearing them for a good amount of time beforehand at different times of the day (feet swell over the day), and also for your normal Sunday walks, bike rides, etc., preferably of course, if you have already hiked with them. The more familiar you are with the shoe, the fewer blisters or pressure points you will have, the more joy the hiking trip will bring you, AND the safer you will be in rough terrain.