The "Outrider" concept is to reduce the damage done by the Staging step. While other decks build armies and gather equipment, this deck scouts ahead and negates threats.
Player 1 will give this deck a ton of cards and resources, using Doomed effects, leaving threat very high. If Player 3 can hit you with The Galadhrim's Greeting early enough, you may be able to throw down some cheap Out of the Wild and Resourceful. Chances are, however, you will not have Secrecy until Turn 2. Use Aragorn to reset at the end of Turn 1, get a little help with threat, and then get the rest of them out. CelebrÃan's Stone is expected from Player 2, allowing Aragorn to play the handful of Spirit cards here.
Use Out of the Wild repeatedly, to remove the worst cards in the deck. Once enough have been removed, Keen as Lances becomes cheap or even free, and The Door is Closed! can cancel the cards that were a problem. Use Gildor's Counsel generously, to reduce staging.
Henamarth Riversong checks the encounter deck to enable Wingfoot, so that Aragorn can quest and then attack, enabling Pippin to draw a card now and again. This combo is a little trickier than just straight-up Unexpected Courage, but comes with the added bonus of seeing one staging card before questing. Also remember Aragorn is sentinel, and is probably your target for A Burning Brand.
Message from Elrond is extremely flexible in this fellowship. In the first turn, you can steal cards from Erestor before he makes Player 1 discard them, and they'll return after the discards. Later, you may want to mail Player 1 a Keen as Lances or two for threat reduction (assuming Campaign mode, when you actually need them to survive). You can mail Player 3 your blue cards if you don't have your CelebrÃan's Stone yet; you can mail Player 3's purple cards to Player 2 for similar reasons; you can send cards to where excess resources are sitting if there aren't enough to play them otherwise. Keep an eye out for what will make the fellowship strongest.