Watching videos of combos is helpful. It's good for knowing what's available but you just have to play to get used to the timing and execution.
To level up quickly, always grab as many quests as you can from town for the dungeon that you are going to. I think there were three modes for each dungeon. Normal, Hard, and Very Hard. Hard opens up after you beat Normal and Very Hard when you beat Hard. Sometimes you'll have to do the same dungeon multiple times to finish quests so always attempt the hardest mode since it gives more experience and better item drops.
If you only need 1 more item for a quest, you can always leave the dungeon but you have to pay ED to leave. This is sometimes good to do so you don't waste a lot of stamina and you can move on to higher level dungeons.
That's my playstyle anyway. If you're new to the game not sure if you can do Very Hard for every map, but the dungeons aren't that hard until you get into Zone 4 and Zone-X in my opinion, which we probably won't have yet.