1) Don't save on the first slot!
Saving on the first slot means your game has to manage through system files to read and write information. Save slots 2 through 9 are saved on the SD card, and thus you can write in a mere fraction of the time.
2) Efficiency Matters
Etrian Odyssey is a series where skills often have "break points" (typically at levels 5 and 10). The skills generally become noticeably stronger at these points, but their costs jump up significantly. Consider leaving the skills at level 4 or 9 early on. as cost does not scale with power 1:1. Similarly, consider alternatives to skills that cost less TP. For example, at level 10 the Ronin's Horse Slash has a 320% damage multiplier for 13 TP, while Swallow Strike cumulatively has 375% damage at 21 TP. That's 85% of the damage for nearly half the cost!
3) Build for the beginning; not the end
On the above note, do not build your characters for the end-game straight out the gate. A common mistake is to try to put your skill points into something that either takes way too many points to get or is unmanageable (too costly or unsafe) before the character is ready. By rule of thumb, if your character doesn't really have any skills worth using by level 10, you should reconsider your build. It's better to build to be strong in the beginning and later rest when you have the skill points for what you want.
4) Staying Alive: A Tale of Two Tanks
Protector or Beast, which should you choose?
Protectors are a mitigation-based tank. They exist to bolster your team's defence, notably against elemental attacks. They are at their strongest when a team is designed to spread damage across multiple members, but at their weakest when you have a lot of high-risk (squishy) party members like front-line Gunners or Alchemists, and struggle to defend both the front and back lines. Protectors are a class with unmatched Vit who should focus on reducing damage to themselves and their party.
Beasts are absorption tanks. They just soak up damage for the party straight up, and can even recuperate damages automatically. They are at their best when a party favours a centralized damage sponge (particularly if you have Ronins, Palm Alchemists, or other squishies), and at their worst when it comes to dealing with attacks that strike multiple explorers at once. Beasts want defence, but as a character with the highest HP pool they really benefit from boosting that HP further with percentage boosts rather than numerical, such as HP Up or Barbaric March. The nice thing about a Beast tank is you can eschew defensive gear on many of your party members if you know no one else will be at risk of attack.
Both tanks can take a little of each other's job with Grimoires, but to a limited extent. For example, to replace Auto-Lick with a Protector, you'll need two Grimoires and only get half the activation rate in the end. Protectors do have better Tec and TP, so they can generally afford some of the more fun Grimoires out there. While Protectors can thus have some cool skills with their more generalized stat distribution, Beasts make up for it with a vastly superior Force Boost. Ultimately you can beat the game with either tank, though if you want to use a Beast, try to get Grimoires with the elemental shield skills somewhere.
You can also go without a tank if your party has a robust enough front-line. Landsknechts and claw-oriented Beasts in particular can take quite the beating, while Highlanders and Survivalists are rather robust as well.
5) Choosing the right healer
With the above in mind, make sure you choose the right form of support. A Protector favours the Sovereign, since their orders provide healing to a whole row anyway; may as well spread the damage out. A Beast favours a Medic; while they can heal the party at will, they have even stronger options for spot-healing, and can keep up with the largest of health pools. War Magi can go either way, performing well with both line and single healing, not to mention Vampire does well in keeping you alive as it is. If you are using an alternative healer like a Troubadour or Survivalist, tailor your builds and strategies with the above in mind.
6) Healers can do more than heal!
Speaking of healers, it should be mentioned that all three of the main healing classes are also excellent damage dealers. Medics have some of the best damage in the game with Vital Strike supported by Barbaric March, and have a deadly speedy stunning staff strike for regular engagements or lower HP compositions. War Magi have a whole lineup of melee attacks, in addition to being able to heal the party hands-free with Artery or while dealing damage with Vampire. Lastly, the Sovereign has incredible efficiency with Link Order; the only catch is they need an elemental attack to followup on.
There will be plenty of times where your party is topped off or the enemy is incapacitated. A healer that just sits around on their thumbs is a serious waste of potential, and you are losing out on a lot of damage by not taking advantage of the tools given to you. At the very least, if they are not attacking, they all have options to boost the party's offence. Use them.
7) Pace your status effects
It may be tempting to pile on Panic and head bind onto the boss on the first turn, but reconsider. Enemies in Etrian Odyssey build resistances to status ailments when inflicted, and it takes ten turns for some of that resistance to subside. It may be better for your Hexer to follow up that head bind with something like Poison or Curse than a debilitating effect like Panic, and wait for the bind to expire. The obvious exception to this is when it comes to binds and other binds, especially if you have a Whip Dark Hunter.
8) Knowing when it's time to burst
When fighting bosses, especially at the intended level or lower, it may be unwise to use your Force Break unless you specifically know you can take it out in under ten turns. A common downfall of people who are playing EOIIU from previous games in the series is they have a low damage party and immediately expend all their resources onto a boss in the first three or so turns, and find they lack the stamina to finish off that last bit of the boss's health bar.
Instead, it may be much more beneficial to go for a full Force Boost rotation. That is to say, to use the Force Boost at the start of battle (without Force Breaking), let the three turns pass, use TP-conservative strategies, and then burst the boss down when everyone has their Force Boosts ready again. This is particularly good for the early-to-mid game with the Sovereign, who can restore TP as you near the finish line.
9) Quest EXP and You
When you turn in a quest or mission, you get a certain amount of EXP that is split amongst your party. Consider using this to feed EXP to rested characters or new additions to your guild by only having them in the party when you collect your reward. This is also a good way to feed EXP to a gathering party if you want more efficient foraging runs.
10) When all else fails; Poison the bastards
Poison damage is absurd in this game. The Dark Hunter's Viper skill and Hexer's Venom Curse put out hundreds of damage, which is strong as it is. However, they almost double in potency when equipped with Grimoires of the same skill. If that's not enough, the Butterfly Tsukudani (which you get early on) doubles poison damage. This leaves you with poison damage cumulatively in the thousands that is suitable for the end game, and will absolutely slaughter regular encounters up until mid-late game.
Worthy of note is that poison's damage is not influenced by any stat in particular, and its damage is derived from the skill that inflicted it plus a small part by the user's level (almost double at level 99). Viper has marginally higher damage than Venom Curse and has the benefit of initial damage, though Hexer's can poison multiple enemies at once and can use their Force skill to make it stick longer.
If you ever feel remorse, remember the countless low-level explorers who have fallen at the hands/wings of Venomflies throughout the series. Bring them vengeance.
