I also can have an over-active mind, which I often find debilitating. Some things I use to help relax more when bushwalking.
1. Take off your watch and put it at the bottom of your pack. You get there when you get there. No schedule to keep now
2. Every time before you start walking again (after a toilet break, after food, after a rest stop) take two DEEP and SLOW breaths and listen to what is around you
3. While it is important for safety reasons to study the route, don't over do it. Checking your progress every 5 seconds (where am I, what does the map say, what should I be able to see) ruins the tranquility and calmness of walking and turns it into an occupation
4. Every time you find yourself counting your stride, stop and sit down until you have relaxed, then start again (subconsciously trains your brain that if you try to push faster, you will end up taking longer)
5. Breathe more slowly when you walk. Counting strides is usually done by people who also breathe in time with their stride as well. If you consciously slow your breathing just a bit, you'll find your walking pace will relax ever so slightly
6. Try and sometimes do walks which are very easy and well marked. If you get in a routine of tough, multi-day hikes you can forget to how to "meander" along.
7. Listening to music is a great recommendation, but choose the right music (peaceful, relaxing). As you walk, keep turning it down one notch every 10 mins or so until it is barely audible. Music is more relaxing when quiet, and that way you will still get all the sounds you came for - wind, squelching puddles, crickets etc.
8. Don't look at your feet if you can help it. A lot of the time I understand this is not possible on uneven, rough or steep ground.
The first time I walked the Loddens I looked at my feet for four hours with my head down. Didn't see a damn thing of what I came to see (nature). By the end of it, I was completely wrecked mentally and didn't enjoy the day at all (and had a raging headache/sore neck). On the way out, I decided not to look at my feet - saw lots of cool stuff, actually walked a bit quicker, but it felt so much calmer and more relaxed.
You are here to see nature so keep your head up as much as possible while walking, but not so much that you trip and hurt yourself!
9. An overactive mind could be caused by not relieving stress enough. Do something silly that really gets your heart racing - the stress relief will mean that afterwards you are more relaxed and will sleep better. A good example of this is to go and jump into a cold stream for a wash after a long day's trudging - initially gets the heart going, but afterwards you feel cleaner and more relaxed/sleep better.