Fire Emblem: The Sacred Stones/Chapter 2: The Protected

Defeat all enemies
Have Vanessa fly across the mountains and rescue Ross first thing. Then have Moulder heal him on the other side of the peaks, and send Vanessa back for Garcia. Meanwhile, have Eirika visit the two villages near the starting point and get the Red Gem and Elixir. Get Seth or Franz (equip a sword to both of them) to ride south to visit the southern village and retrieve the Pure Water before a bandit pillages it. After Garcia is back on the west side of the mountains, talk to him with Ross and send both of them south with Franz or Seth (whichever one you didn't use to get to the village). Leave Eirika, Moulder, and Vanessa behind to deal with the reinforcements that will appear north of the village on turn 3. After they are taken care of, have them join Garcia, Ross, Seth, and Franz near the fort. Fight off the remaining bandits, and keep out of Bone's range until he has gotten out of the mountains.

Boss: Bone
You could wait for Bone to walk down, or try attacking him with Vanessa. She won't do much damage, and will probably have to go back to be healed each turn, so it's hardly worth it. Instead, wait for Bone to get to the ground, then swarm him with Garcia, Franz, and Eirika. Try to whittle down his HP, then use Ross to finish him off and get a lot of experience.