Based on what you've written I'll make a couple of suggestions as a former track sprinter, collegiate cyclist, running/endurance coach and triathlete.
1. Set a defined goal that is time bound. Such as, "My goal is to run 5k without stopping by April 30th" or "My goal is to get from 8:00 mile to a 7:00 mile in 6 weeks". This will help keep you honest and focused. How you train will depend on what your goal(s) is (are).
2. Footwear is very important, don't go cheap. Just like on your car, quality tires matter and the same goes for running shoes where the "rubber meets the road" or trail. Every time your foot hits the ground you are absorbing a force along the lines of 3x your body weight. A running store and gait analysis is probably a good place to start if you don't know what shoe to get but understand you may have to tweak things based on your training schedule and running style. It is not a perfect science. Listen to your feet. I also highly recommend bodyglide if you are prone to blisters and pay attention to socks as well. Get a few pairs of good, close fitting running socks.
3. Trail and road running are very different. Trail running has a lot of uneven surfaces, obstacles, changes in elevation, steep inclines and declines which tax the body differently than a flat 5k. Regardless, start slow - but start even slower on the trail. However slow you think you need to start, start even slower than that.
4. Vary your training in distance, intensity and terrain. You will be much more effective with a varied training regimen as opposed to just getting out and running the same 2 miles at the same pace every day. You will get bored, your progress will be slower, and your body will not adapt in an ideal manner doing the same thing day in and day out. As far as programs go, there are lots of them out there for free, or they can be purchased relatively cheaply. Group runs from your local running store are also a great way to make friends, get in a recovery run (or fast run, depending on the group) and ask questions.
5. Don't neglect recovery. Warmup, stretch, foam roll, cool down are all very important. Incorporate a recovery run into your training schedule and be religious about keeping it a recovery run.
6. Incorporate barefoot drills. My athletes may have thought I was weird for this, but they all got faster. If you're just starting out, a few 100's on a soccer field will suffice as part of a warmup or cool down. This will build strength in your feet, ankle, and lower leg. Weak feet being coddled by cushy running shoes is the cause of many a running injury.
I could go a lot deeper but that's probably good to start getting the wheels turning. Happy trails!
