If you've only just picked up Bravely Default, we have a whole bunch of tips to make your experience better.
Do all of the sidequests — at least in Chapters 1-4.
Every time you see a blue exclamation point on the map, that's a side quest. Don't think of them as optional activities, though. You'll want to hit them all. Much of Bravely Default's story is told through vignettes and interactions that occur outside of the main plot, so from a narrative perspective they're essential. They also unlock new character classes, so from a mechanical perspective, they're also essential.
As for the latter chapters — well, things start getting a little repetitive, so I won't blame you if you start skipping side missions then. At the very least, do every sidequest the first four chapters.
Don't be afraid to turn off random encounters.
Bravely Default comes with a menu full of useful toggles including a random encounter slider that lets you turn off invisible battles entirely. Don't be afraid to do this. At first, it seemed like cheating when I used the random encounter slider to clear dungeons, but once I got used to that Game Genie-esque feeling, I loved the rhythm of being able to fight battles at my own pace. Because SCREW REALISM.
Just one or two levels can make a huge difference.
Stuck on a tough boss? Try a new job, or just go get some more experience — Bravely Default is balanced so that one or two levels can make a massive difference, so don't give up hope if a boss demolishes you the first time around.
Optimise your time if you're gonna grind for levels.
You will have to fight random battles to get past bosses, whether you're fighting them normally, as you progress through dungeons, or in batches, grinding outside of a town. If you decide to do the latter, make sure to speed up combat (with the right and left directional buttons during battle) and make liberal use of the auto-battle tool. Grinding ain't so bad when it goes by quickly.
Make sure to "update data" once per day.
In the save menu, there's an option called "update data" that lets you recruit random Internet people to work in your village and help you out during battle. Use it every day! You can get three or four new friends every 24 hours, which is particularly helpful if you don't get a lot of StreetPasses wherever you live, or if you have no friends.
Don't forget about Norende Village.
If you want to be able to buy bonus items — some of which are totally killer — you'll want to rebuild the village at a regular pace, so don't forget to put your people to work as often as you can. Also...
Leave the game in Sleep Mode when you're not playing.
Not only will your Norende villagers keep working while your game is in Sleep Mode, you'll also gain points that can be used for extra attacks in battle. (You can also buy these points via microtransactions, but why would you ever want to do that?)
Stock up on accessories that block against status effects.
Some bosses can do some really nasty things to you with effects like Poison and Charm, so toward the end of the game it's uber-helpful to have four of each status-blocking accessory, like the Star Pendant and Rebuff Locket. You won't need a full slate right away, but horde them as you get them.
Never be unprepared for a dungeon.
Always have at least 10 of every major item — potions/hi-potions, phoenix downs, ethers, etc. Always have a teleport stone, too, just for your own convenience.
If you're stuck in a dungeon, turn off random encounters!
Down on magic? Low on HP? Out of teleport stones? Don't forget that you can turn off random encounters.
Don't neglect your characters' support abilities.
It's easy to forget about passive skills, but they're essential later in the game, and they can always make boss battles way easier. Don't ignore them. Every time one of your characters gains a job level, go check out what new skill he or she has gained, and equip as necessary. Eventually you can turn some characters into machines — for example, a healer with Holy One (raises effectiveness of healing magic) and Epic Group-Cast (makes spells just as powerful on groups as they are on individuals) can be borderline unstoppable.
Play around with your special attacks, too.
Don't ignore the "special" section in the menu — you can use that to customise your characters' special attacks, adding elements that make them even more powerful. (You might notice that there are a lot of ways to make your characters really powerful in this game.)
Make Edea a fighter.
When I first started, I was tempted to turn my two dudes into fighters and my two women into mages, because I have succumbed to Big Sexism. But really, Edea makes a much better physical attacker — give her Knight or Ranger or Ninja abilities to turn her into a genuine killing machine. She is the best.
Listen to the party chats.
They're fun. Don't miss them.
The music is too good for the 3DS's crappy little speakers. Seriously.
Experiment with jobs, and don't be afraid to get creative.
Every character has one primary job, but you can actually set their secondary skill to another class, like in Final Fantasy V or Tactics. Just go to the Ability section of the menu and select "Job Command."
Want to turn Ringabel into a Spiritmaster/Ninja? Feel like Tiz would make a good Ninja/White Mage? DO IT. Bravely Default's job system is really flexible, and it's really easy to mix and match skills. It's best to start experimenting early, so you know exactly what your characters are capable of when you get to the harder bosses and you have to find optimal strategies to take them down.
This is a tip both for Bravely Default and for life as a whole.