Part of Devious Dungeon is attacking then jumping away to preserve your health. In the later levels, you'll be confronted with more monsters so you'll have to plan your attacks as they move in for the kill.
It pays to search every dungeon thoroughly just in case you find a secret area. Suddenly the walls become transparent, and you'll see things like extra treasure chests and books that give you a big chunk of experience points.
Olaf's Emporium lets you upgrade your weapons, armor, rings, and amulets, and you can buy potions for extra power. You can also buy coins for real cash, but I never had a problem earning them on my own.
Within each themed world, there are 10 dungeons, with portals you can warp through at three level intervals. This means if you make it through the second of three dungeons in that group, but die, you'll have to start over from the one you can warp to.