Fire Emblem: The Sacred Stones/Walkthrough

Prologue
Try using Eirika for the two lesser enemies. She should be able to take them out without dying. After she uses a vulnerary, have her tackle O'Neill.
 * Objective: Defeat all enemies
 * Allies: 2
 * Recruits:
 * Eirika (Automatic)
 * Seth (Automatic)

Boss: O'Neill
Try having Eirika tackle O'Neill. If her HP drops below half on his counter-attack, have Seth rescue her so that she can heal and attack again.

Chapter 1: Escape!''
Have Eirika take out the Fighter near the starting point, then wait for Franz and Gilliam to arrive. Once they do, have them Eirika join Gilliam in the middle of the map and have Franz go to Seth near the starting point, because a group of enemy reinforcements will arrive there. Have Eirika take on the two fighters in the southwest corner, and use Gilliam attack the two Soldiers near the gate without leaving him next to Breguet. Then, have Seth and Franz join the others at the gate.
 * Objective: Seize the gate
 * Allies: 2
 * Recruits:
 * Franz (Turn 2)
 * Gilliam (Turn 2)

Boss: Breguet
Take a look at Breguet's attack and Eirika's defense, keeping in mind that he'll get a bonus against her because of his lance. If you think Eirika can take him without getting killed, do so, and rescue her with anyone if necessary. If not, try using Franz, who Breguet won't have an advantage against. If worst comes to worst, use Gilliam, who can definitely take a few hits. Don't use Seth.

Chapter 2: The Protected
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.
 * Objective: Defeat all enemies
 * Allies: 6
 * Recruits:
 * Moulder (Automatic)
 * Vanessa (Automatic)
 * Ross (Neutral; talk with Eirika)
 * Garcia (Neutral; talk with Ross)

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.

Chapter 3: The Bandits of Borgo
Send Neimi up to speak with Colm when he appears at the end of turn 1. Have everyone else break through the cracked walls of the two rooms east of the starting point. Defeat the bandit in the southern room, get the javelin from the chest, and use combined direct and ranged attacks to take out the bandit in the north room. After, use the door key to open the door between the two rooms and send everyone up without straying into the bandit in the northernmost room's range. Have Colm, Neimi, and another weaker character take out that bandit, then send everyone but Ross and Franz (who should have been given the javelin) into the room. Get Colm to steal the contents of the room's three chests, then distribute them to your units. Meanwhile, get Ross to take out the Brigand on the other side of the cracked wall while Franz attacks the Thief below him. If the Thief survives until your units enter that main room, he'll steal all their loot, and you'll have to get Colm to steal it back if you want it. Once the western side of the main room is cleared, break the cracked wall on its west wall and have Colm open the door in its north wall. Storm in and defeat all but Bazba and his bodyguard. Then have your weaker units and one strong unit position themselves around Bazba.
 * Objective: Seize the throne
 * Allies: 9
 * Recruits:
 * Neimi (Automatic)
 * Colm (Neutral; talk with Neimi)

Boss: Bazba
Bazba's tough. The good news is that you can attack him from six spaces. You'll probably want to use Neimi, Ross, and Garcia to attack with the iron bow, hatchet, and hand axe respectively, all from two spaces away. Equip a sword to Franz and have him attack from one space away. Do the same with Eirika, using the rapier if necessary. Keep Seth in the background in case they can't all topple him in one turn, because he'll probably counter-attack against Neimi with his hand axe and kill her. Keep Gilliam and Vanessa away; they have a very low chance of hitting Bazba.

Chapter 4: Ancient Horrors
This is your first chapter with the preparations screen. Choose your units wisely, for two of them will have to sit this fight out. Colm can't do much for you here, and Ross may be a liability if he isn't significantly leveled up. This chapter pits you against monsters, which are a group of enemies that will become common in later fights. If you want to get Lute quickly, have Vanessa fly across the river and use them to take on monsters on the island. If you want to level them up some more, use Lute's ranged magic to fell the snag on the river's opposite side, then rejoin your companions. Meanwhile, split the bulk of your party up into three groups. Have two strong units like Gilliam or Garcia take out the reinforcements that spewed from the northwest corner when Vanessa crossed the river. Have one mediocre unit go south and help Lute and Vanessa with the monsters above the river. Have the other four units go east and destroy the three monsters and the three reinforcements. Arthur could probably take them all, because his light magic is effective against monsters, but you could use weaker units in conjunction with him as well. After that, have all of your units ford the river and assign one or two to each of the non-boss monsters on that island.
 * Objective: Defeat all enemies
 * Allies: 9
 * Recruits:
 * Arthur (Automatic)
 * Lute (Visit the southern village)

Boss: Monster
The boss of this chapter, which is an Entombed, has a lot of HP. Use weaker characters to swarm him, but make sure that they won't get killed on the counter-attack. Keep Arthur nearby in case things go badly.

Chapter 5: The Empire's Reach
You have to bench four of your units this time. Again, Colm isn't very useful, and you might as well give all of Moulder's stuff to Natasha, as she has to fight in this battle. At the start of the fight, send Seth down to the village in the southeast corner, then have him and one other unit deal with the bandits north of there. Split your party into three from there. Have Eirika go to the middle staircase and wait. Have Garcia, Franz, and Lute go up the left staircase and take out the enemies in that street, as well as the Archer on the other side of the wall. Have them wait near the armory, and stock up on equipment if necessary. The rest of your units should lure out the Soldier and the two Fighters in front of Joshua, weaken them on the counter-attack, then finish them off on your next turn. Recruiting Joshua isn't hard once you've taken out the soldiers. Natasha won't get attacked. Just go put her near him then.. duh.. At this point, you should have had Eirika take out the Fighter next to the vendor and the soldier in front of the village. Visit the village while Joshua takes the brigands near the arena out. Send the left-side party east to visit the village and attack the enemies around Saar. Once Saar is the last enemy, you can have Joshua visit the arena with his killing edge. Chances are he'll do better than he did before the chapter began.
 * Objective: Defeat the boss
 * Allies: 9
 * Recruits:
 * Natasha (Automatic)
 * Joshua (Enemy; talk with Natasha)

Boss: Saar
Equip the armorslayer to Joshua and the rapier to Eirika. Have them both attack Saar on the same turn, and he should go down against the two effective weapons. If not, have Ross waiting to make the final blow.

Chapter 5X: Unbroken Heart
Charge in, you won't lose the characters. Take all Orson’s stuff and give him a Javelin.
 * Objective: Seize the throne
 * Allies: 4
 * Recruits:
 * Ephraim (Automatic)
 * Forde (Automatic)
 * Kyle (Automatic)
 * Orson (Automatic)