I am reading these posts and seeing that a good amount of people are struggling on some of the earlier levels (Between 5-7 seems to be the big ones) and for some reason, I feel really nostalgic reading this comments xD. I have beaten every US Released Fire Emblem multiple times and there are certain play styles I have found that work better for these games, espically levels where you are trying to recover a unit. Here are some tips that should help you guys.
1) Always play defensively! This is the biggest help I can give to people. Playing offensively hardly gets you anywhere in the game. If you are in doubt about moving a unit to get a single kill, don't make that move. Allow the enemy to come to you. The AI in the game is very aggressive and if you just take the levels slower and allow the computer to make the moves, you will see more victories and less restarts.
2) Travel in squads! Its always good to split your team into 2-3 units and give each an objective depending on enemy placement or goals. Makes sure to arrange the team for certain situations. Personally, I usually split my team as the fallowing: one squad is mainly my hard attackers with 2 healers and usually has a max of 6 units totall. The rest of the group stays together and travels the easier route, and I usually have the more defensive units such as Padalins and Generals in the slower unit. I try to mix the first unit to, such as one Mage, one healer, one flyer, 2 healers to cover each other and two physical attackers such sword masters, Heroes, Padalins, ect.
3) Know the enemy and plan ahead! Not many people know this, but if you "a" on an enemy unit, it will show you where the enemy can move. This is key when are making your moves and deciding how many squares you should move. If you hit "L", then you bring up the enemy stat sheet, allowing one to see what weapons the enemy unit has. Also another good tip is if the boss is defending a post or check point, he will not move, so never worry about bosses getting the best of you. You can simply use the rescue command the pick up the injured unit and move them to a safe location next to your healer.
4) If you are trying to recruit an enemy unit, easiest way to do it is like so: first eliminate all the guys around him, leaving him by himself. After that, take a character that has really good defense and resists there weapon and place him in the enemy units kill zone without holding a single attacking item (I always used seth in the early levels because even crits from characters can't kill him early on). The next turn, the enemy unit should approach the helpless unit and attack them. If all goes well, the character should live the blow and it leaves you free to recruit them as you please.
Thats the basic jist of things. If there anything else someone is stuck on, let me know and I will reply with something to help. Good luck guys!