That means not being a KILLER, because that is what a fighter is. A ranger is a SURVIVOR. That involves killing, of course. And running away, too. And keeping friends who have your back. It means knowing your environment and gathering knowledge before you act. In war, being brash might make you a hero, but in the wilds, it just gets you killed.
D&D Classes Without Math: The Ranger
Here are my core features (without math) for the ranger class, in no particular order:
1. A ranger is best equipped with leather armor, a bow, and some knives.
Lugging a 5 pound longsword through the woods is both exhausting and stupid. Bringing a matching shortsword along with it is downright lunacy. The ranger has two modes of battle: safely from afar, or up close and personal. Ideally, a few arrows in an unsuspecting target ends things before they begin. However, if a wild animal or monster gets the jump on you, your best bet is always a knife: easy to carry, easy to conceal, easy to draw, and easy to use. Not to mention it has about 1 billion different uses when surviving in the bush. I could hear an argument for a light axe, but again, it's a matter of weight vs. utility. Of course, I would never tell my player "You can't wield that" but giving the ranger a nice bonus to bow and knife attacks certainly implies "Why aren't you wielding that?"
2. An animal companion is a must.
This is perhaps the worst aspect of the 5e ranger. The fact that animal companions are so downplayed as to be near useless is super disappointing to me. A ranger's companion is the best tool in their arsenal, and also the thing that keeps them sane. It is impossible to have any serious human relationships in the wild....alone....all the time. Your animal is your best friend. I don't care what you have to cut, feature-wise, from your ranger class. Just get a good animal companion in there. Let it act freely as a pseudo-second character that goes when the ranger does. There is just about nothing more unique to any D&D class than a ranger and its companion. (P.S. I'm very much against druid animal companions, for various reasons, not the least of which is that they can already shapeshift into nearly any animal they want.)
3. IT'S A TRAP!
Traps, man. They have been disabled for years by characters, but never set by them. Why? Rangers need certain kinds of traps (mostly snares) to eat. As the wardens of the woods, they would clearly also know how to set traps for larger (read: humanoid) trespassers. Digging a big pit trap might be a bit much, but I think a ranger should be able to make a rudimentary branch-spear trap given an hour in a suitable natural environment. And noise traps! Noise traps would be huge for any ranger leading a group through an area where they will have to make camp and sleep. If you don't know, a noise trap is something like a bag full of empty tin cans falling from a tree when someone trips a trap wire. It isn't meant to harm anything, just make a bunch of noise. The noise will alert you as to the creature's presence, and also its direction and relative distance. Traps allow the ranger to be creative during downtime. Always a plus. Rangers should also be able to spot such wilderness traps, if they are careful.
4. Bush medicine.
Rangers get nasty wounds out in the wild and there is no one around to help them. If they didn't sew it up and clean it themselves, they would surely die of blood-loss, infection, or both. Just so, rangers should be one of the most, if not the most capable healers in the party. This can be as simple as being able to stabilize a dying creature without needing to make a check. It could be a scaling ability that eventually includes treating poisons and diseases. You chose. Point is, a ranger that knows nothing about basic first-aid is a dead ranger (and even worse, a boring ranger).
5. The little things.
This is another grab-bag category where you might want to fill stuff in. Tracking, for instance. If you don't let non-rangers make tracking checks, then rangers are automatically that much cooler and more useful. Maybe rangers should be immune to surprise? Those wild instincts are one reason why he/she is still alive, after all. Camouflage and hiding abilities could also be useful, though I think just being silent is more the ranger style. The great outdoors provides plenty of easy cover and hiding spots. Hiding in an open area that is being observed and such is a thief/rogue tactic, if anything.