I've lived in Berlin for a little over a year, and it took me almost as long to discover this trail. It's kind of sad that it took so long, because now it's my favorite bike trail, running trail, and attraction all in one. I live in the northeastern part of Berlin, and just stumbled across the sign one day, pointing to a path (partially obscured by some trees) that I wouldn't have otherwise noticed. I took my bike down the trail, and was hooked. I guess it depends on where you start the trail to gauge what type of ride or jog/walk you'll have. I started close to the outskirts of town anyway, so soon I was riding through beautiful meadows lined with hay bales, I saw people riding horses, dogs swimming in a little stream, and huge farms in the distance. I even passed a swamp at one point.
A few weeks later, I started the trail closer to where I live, and took the opposite direction towards Mitte. I crossed Bornholmer Straße, winded my way through Mauer Park, passed the monument at Bernauer Straße, and eventually made my way to the area by Hauptbahnhof before I turned around. There are so many beautiful sights in and around Berlin to see, and quite a few are sights I would have never seen were it not for being on the Berlin Wall Trail!
As you navigate the trail, you do have to change directions, sometimes quite frequently. The gray signs for the trail are kind of small, but they appear fairly frequently. There were a few times I had to turn around to figure out where I missed a turn (at least five times). There are maps online to help you map the trail, http://mauerweg.com/mauerwegkarte.php
But this website isn't the best. If you have an iPhone, I would take screenshots of my gps location every twenty minutes or so, when I knew I was on the trail. It was helpful when I lost my way. It was also great to have my smartphone to snap some pictures. On Instagram, you can use #berlinermauerweg or #berlinwallwalk to link your pictures. Slow Berlin recently did a feature of this trail in their weekly newsletter, which I thought was great. I see lots of people on the trail, but lots of them just think they're at Mauer Park or just visiting Bernauer Straße. They don't realize that the trail spans almost 160 km in and around Berlin.
My tip would be to find a bike and take yourself to an SBahn station that's near the trail (Bernauer Straße, Pankow, Eberswalder Straße is close to Mauer Park, and Wilhelmsruh are the ones that first come to mind). Just check the map of the trail for the location closest to you, and then go explore! If you start in the city, it may take quite awhile to get to the countryside, and vice versa. Bring water and SPF!