A nice, well maintained and groomed trail is a favorite any time but especially when starting out so you don't come up against things you might not be ready for.
Having a good general fitness base is important, but you also need to be in "hiking shape". Hiking for miles takes its toll on your feet and a day pack will give your back a bit of a workout too. Plus, water is generally heavy so that is something to consider when going out for a hike. Not saying don't take water, just need to be ready for the weight. Although the good news is the water weight goes down as you drink it.
I disagree with the poster who suggested starting out with a 10 mile hike. That seems a bit long, IMO. Maybe 3-5 miles in an area near you that might offer some elevation gain and loss, 100-200 feet or so, nothing real significant but enough to test you and your gear a bit. Don't skimp on hiking shoes/boots. Get properly fitted and check about a return policy. REI, for instance, will take back used equipment so they are a great place to buy footwear. Good socks, another must. I use sock liners as well to help keep blisters away. They can happen even with perfectly fitted shoes and good socks.
Another good thing to have is a goal of some sort. Perhaps you are getting ready for a hiking trip, or just want to be able to hike long miles and at some elevation too. Start out easy, at first, and work up to the more difficult hikes.
Maybe a bit more info than you asked for, but hiking really is more than just how long and what trail.