DO'S

1.  Do always refill on water when you have the chance.
2.  Do pack a cell phone on your runs.
3.  Do turn off your cell phone when you don't have service, otherwise your battery will eventually drain as it continually searches for a signal.  
4.  Do give rattlesnakes their space.
5.  Do plan on a run lasting longer than you expected.
6.  Do plan on rain when you didn't expect it.
7.  Do expect an easy run to be hard.
8.  Do expect a hard run to be easy.
9.  Do pack antihistamines in case of bee or wasp stings.
10.  Do tell someone exactly where you are running (& keep to it).
11. Do pack toilet paper!
12. Do pack calories, even if you don't think you'll need them.
13. Leave phone numbers at home of people you are running with.
14.Do stay in the moment!
15. Look before you sit. ALWAYS.
16. Smile
17. Kick out the back (to begin, you won't trip on rocks that way).
18. Pack gloves (just in case!)
19. Do stash water on your regular trails, or know some who does and has given you permission to use their stash.  Helps a great deal -- just in case!
20. Watch where you step (so you don't stomp on those cute little salamanders, or caterpillars, or whatever it may be, perhaps a rattlesnake?)
21.  Do over pack.  I know there's plenty of believers in under packing.  I am not one of them.  I prepare for the odd thing, like I sprain my ankle and fall into a gully off the trail where no one can find me.
22.  Do pack:  (aside from calories, fluids, gloves, phone, toilet paper, hat and sunglasses):  electrolytes, a lighter, a knife, a bandanna (which can be used for many things), band-aids,  ice on a hot day (it won't last long, but will be useful in the beginning).  I also pack an extremely loud whistle and pepper spray, a tiny container of sunscreen and also a tube of Glide (for chaffing.)
23.  Do always tell those that you love, that you love them.
24.  Do tell people who warn you that trail running is dangerous that getting on the freeway is dangerous as well.
25. Do smile and acknowledge other trail runners, hikers, bikers.
26. Do try and beat that mountain biker up the hill, but act humble when you do.
27. Do help out a runner/hiker/biker in distress.
28. Do try and eat some breakfast, even if it's early, early in the morning.  I usually go for a glass of carrot juice, which I find delicious (a lot less than 200 calories).  If I have a little more time, I go for a piece of whole wheat toast with peanut butter (YUMMY), and if I have all the time in the world, I go for either 2 boiled eggs, OR 1 egg  (boiled or scrambled) with a piece of whole wheat toast. 2/2/21 Edit: I no longer eat breakfast (ever) unless you think of breakfast as merely your first meal of the day (breaking your fast) which in that case I do eat around 2 pm or later.
29.  Do be careful.  People die on the trail, sadly.  Keep your wits about you.
30. Pack Glide or some other anti-chaffing remedy for long hot runs (maybe I've mentioned this).
31. Pack water in your car so that if you returned dying of thirst you can gulp down.
32. Do accept the gnats.  That's the only thing you can do about them.
33. Do find shade to rest in when you feel overheated.
34. Do hike the hills when you need to.