Use the calendar to catch story events: Cai training retreats, chest saves, and Chapter 12 preparationMinor spoilers
Track paralogues and hidden events together. Save before obtaining random chests, and prepare promotion licenses and war-campaign weapons while leveling.
Original video: Cai route’s incredible leveling bug! Hidden scenes you should not miss! Six essential tips for Fire Emblem: Fortune's Weave | Bilibili creator Yingming Xinzhao
Mark paralogues and hidden events together
Recruitment, paralogues, and hidden story scenes are easy to miss early on. Focusing only on paralogues can make you forget a hidden event in the same chapter and require replaying. Combine both event types in your notes and mark them ahead on the in-game calendar for reminders.
I recommend 
Dietrich, 
Leda, 
Theodora, then 
Cai. If you already started Cai, finish experiencing the tutorials, play the other three routes, then return to Cai. Cai has few early units, later class access, and transport restrictions. Cross-route experience makes playing him later easier.
Leave an enemy and retreat from instruction battles to level repeatedly
- 1Enter Cai's training battle and leave one enemy alive in the final wave.
- 2Retreat, then reenter training.
- 3Keep fighting, leaving an enemy and retreating again before completion.
This accumulates levels, class experience, weapon experience, and animal bond without spending free-action turns.
Buy advanced licenses and unlock classes early
Experience bonuses from multiple routes can raise levels quickly before the town sells advanced licenses. Once the map opens, buy 
Advanced License in the royal capital Megaira and check again at each chapter’s start. Restock from the seller beside class changes when their inventory updates too.
Playing Dietrich first also unlocks 
Ranger, giving later sword training another class with strong growths.
Save before obtaining random chests
Random chest contents are determined when acquired. Saving after purchase and reopening still gives the same item. Save before buying or exchanging, then obtain and open the chest. If the result is unwanted, reload and buy again.
This can provide anti-cavalry weapons early. Advanced chests may also contain 
Cleansing Blade and gems. Outside Cai’s route, later routes can use carriages after reaching the world map to buy later-area weapons, then return to normal progression.
Build support and finish equipment in Chapter 12
Once the roster is complete, take a mage into the mine outside town and use magic once. Then visit the feast point and repeatedly choose meat feasts to build team support. Restart the chapter when the date arrives to continue training.
Each protagonist has different support conversations, so arrange this on every route. Some advanced conversations still need extra gifts and meals. Unlocked conversations can be replayed in the hall.
Before the war campaign, gather weapons for different jobs: 
Zanbato, Cleansing Blade, Levin Sword, 
Hammer, and the Da Mina series. Buy what you need when available. Stop hoarding skill manuals. Use them on the right units in Chapter 12, with black- and white-magic manuals going to mages.
Find slightly higher-level dungeons in the list
In town, press ZR twice to open the continent map, then switch to the dungeon tab. Recommended levels, chest counts, and collection status are visible, helping you find what is missing.
For leveling, choose a dungeon slightly above your team. Let high-level allies assist while lower-level units take kills. Retreat if HP runs low or enemies are too strong, then return after enemies refresh next chapter.
Dietrich can repeatedly draw enemies, while the other three routes need to value equal- or slightly higher-level enemies along the road. If short on 
Giants' Meat, find the giant at Sand-Shadow Fort rather than waiting indefinitely for random map refreshes.
