Fight! It’s so tense and fun!
Sorry, I sold my soul to the Prince of Battle and am now obliged to recommend Fight! at every opportunity.
What’s the campaign? What are you all doing in the game?
Situations where response times and terror reign are Steel’s bread and butter. It also playes into Intimidation attempts (and the therefore the Duel of Wits.)
It can also be used in any instances where mental fortitude or drive is in question – Can you bring yourself to murder this person in cold blood? Can you suffer through the pain long enough to do what you want to do? Etc. Will can be used for some of these too, I reckon.
Steel is pretty lightweight and easy to use, so you’ll likely not want to cut it out to save on processing power.
Resources is just really fucking cool. It’s going to add to games where finances are concerned. It’s deep and engaging enough that I always want to interact with it in every game I’ve played.
Not only does it give you a “Can I buy shit” mechanic; it also ties into some longer-term systems and helps pace play. The maintenance cycle introduces tension to long-term, “Years, pass,” style of play where extensive practice and long-term tests will wear down your Resources. Then it’s a matter of working to rebuild your Resources, and that takes time (and may reflect anything from farming to guarding caravans with your blade to managing your estate).
New players often look at how you get taxed by failing Resources tests and say, “What!? I lose money when I don’t buy the thing?” If you find yourself in that position, I refer you to The Gift of Kindness on page 370.
Circles is also really cool. I can’t think of a reason not to include it in every game.
Some stuff to watch out for is players (and GMs) often have a difficult time wrapping their heads around it. Remember that characters have to do something to test the ability – they need a task. Do they ask family? Do they go to an acquaintance’s house? Do they send a letter?
I’ve seen GMs get a little excited about the Enmity Clause magically turning contacts and acquaintances hostile. That’s not often called for. If there’s good connective tissue for that result (“They found out about that thing you did last session.”), fine. But note that you aren’t restricted into introducing the sought-out character as an enemy. I had a player want to go to an inkeeper that would give him a free room for a few nights; when he failed, he went to the (firendly) innkeeper just as they were being extorted by a local underworld tough who did not let him stay out of it.
Drifting into Reputations and Affiliations, require real color for those dice, and apply that color to each test they’re used in. If a player wants to circle from their military unit, they get a military person. If they don’t want a military person, they shouldn’t use their Affiliation dice. If they use a Reputation, they people brought into play know them by that Repuation.
Relationships – get invested in them as the GM. They are NPCs important to this game; treat them just like that. I’m looking at you, me. 
I definitely recommend regularly using at least one type of conflict system in your game. If you don’t want combat, Duel of Wits it is.
I often see new people start the Duel later than is ideal. They talk back and forth over and over, and then, once the Duel starts, there’s nothing left to say. Actively resist that. All of you stay vigilent for social conflict, and, once you spot it, deliver your Statement of Purpose. Say, “If you don’t surrender this castle to me, you’ll have to contend with my lord. You don’t want that. That’s my Statement of Purpose. Duel of Wits, motherfucker.”
Conversely, try to make sure that both parties want something from the other and are in conflict. Speak in character exploratorily. Don’t be afraid to prod arround the conflict to find out where it really is before dropping the “motherfucker”.
Little bit of a pro-tio: Look for FoRKs before you speak your part, then speak them into your part, then ask for the ones you spoke, then roll the fucking dice. It can be real easy for people to go down their list after the fact, “Sword-wise?” “No,” “Maybe I can make a sword metaphor, hold on…” Just roll the fucking dice.
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