If you don't already have hiking footwear and/ or a backpack, test them out to ensure that you will be comfortable with the fit of each. You could go to a bigger store and try things on, then look for a better deal online. I particularly like how REI has some faux rocks in their footwear area to simulate going downhill.
Trekking poles take stress off your joints and help with balance.
There are also a number of apps with trail maps that enable you to use your phone as a GPS. Just remember to download your digital maps and bring a charger! Cell signal can be nonexistent in the mountains, and you don’t want to lose power.
Always be prepared for changes in the weather!