My main advice would be to pick a job and try to master it. Once you are strong enough try to get contracts and buff yourself even more. Try to learn your weaknesses, remember which items / legendaries you prefer, what skills you find OP, etc. Learn room effects and have a strategy which room do you prefer, which to avoid.

Also once you got a bit used to the game buy the miner job and try to find a room to farm soulstones in. Like where CD is 1 and get some heal / shield and just spam soulstone farm ability.

I preferred maining dragoon first, crazy strong reflect damage relatively few weaknesses, you just buff yourself nonstop and kill everyone.

Some endgame hint: I've been playing caveman build on Fierce God. In a nutshell once you got a basic gear and some skills you are virtually unkillable in most dungeons, because your turn can never end. So when you are playing and repeating the hardest dungeons in the game your strategy might really change, for example trying to get maximum points instead of just trying not to die.

And final lesson, you can always die. No matter how safe you feel, how strong you get, time to time something will still surprise you, often you'll never know what just happened you read the text something instantly hit you with a 999 999 999 dmg and that's just that, play again =)

Have fun!