With the new recon ranger promo, the community finally gotten a better look at these elite soldiers. Sorta. The new flavor text has revealed quite a bit about the rangers, and much of it is rather surprising.

First off, the rangers are far more expendable than one would expect. The fluff text indicates they have an extremely high mortality rate, likely because of the nature of their duties (which are beginning to look less like recon and more like guerilla warfare. But more on this later). The rangers also have a very "only in death does duty end" vibe about them, with the Bitter End and spikes showing that they are encouraged to fight to the limits of their endurance, and spite their foes even as they lay dying. If you're familiar with warhammer 40k and the Imperial Guard, some bits of the rangers may feel very familiar.

Secondly, the new items shine a light on the missions of the rangers. Danger missions already showed that they perform operations that would not usually be called recon (Desna is clearly a believer that recon doesn't mean the target should be left standing after the mission is complete). Their helmets are designed to intimidate foes, a design feature that recon troopers wouldn't need (since they try not to be seen, rather than scaring those who do see them). The recon rangers are evidently much closer to the US army rangers (elite light infantry who frequent scout out and then attack hostile targets), with a good dose of grimdark tossed in.

The upshot of this info is that it makes it easier for us fanfic writers to portray the rangers. Here are a few tips I suggest following:
1. There are 2 kinds of Rangers, badass and dead.
2. Given the high death rate, they've likely developed a very grim sense of humor as a reaction, along with a more stoic, determined personality. "lighthearted" will not be a fitting description.
3. Jaded as all get out, with a healthy dose of fearlessness on top. Theyve seen everything, killed it, and then found something worse. If you have rangers encounter the swarm, I had better not end with them running in terror.
4. Intimidating, to friends and foes alike. These people find the idea of welding spike to their armor as a final insult to their foes an entirely normal thing, and have seen so much crap that things that will send a regular knight steaming in horror won't even register on a ranger's "scary thing o-meter". Put all that together, and you have one scary person. They probably don't even need the skull hats at this point.
5. Sense of superiority. Rangers go where others won't and do things others can't. They will (rightly) consider themselves the best the spiral order has to offer, and they will let other knights know it.

There will be other common traits, but these 5 will be more or less universal, unless the knight in question is very new (and I wouldn't put money on him lasting long enough to become more ranger-like. But his comrades probably will).

Ranger Creed
We are the Recon Rangers
We go where others cannot, do what no one else can
We have gazed into the abyss, and it has gazed into us
We have faced the darkest depths of the clockworks, we have confronted the terrors within
We are the things that go bump in the night
When our enemies lurk in the shadows, we charge in after them
We are the Rangers
We are the best of the Spiral Order
And we shall know no fear