Buy armour whenever you can afford it as it will effectively double your health.
Avoiding damage
Most of the damage you will get will originate from accidentally colliding with enemies, which usually are slimes, that appear from the ground. Watch the ground and make sure that your character stays away from nearby slimes. Jump if necessary, however you can usually just time your movement in order to run directly into them with your weapon.
Carve out a space
If you can dominate one side of the screen without worrying too much about everything at once, that will make survival easier.
Combos
Each enemy killed will increment your combo count by one, and slightly increases your meter. If you can kill another enemy before the meter empties, your combo will increase. The higher your combo, the more fame points each enemy kill is worth. Try to keep a long combo going, to gain a lot of fame points. Taking damage will not reset your combo count.
Defeating the Imp
The Imp is the level 2 Boss. He teleports to either side before shooting an energy ball, which moves in a straight line or in a curved pattern. The direction it is shot depends on where the Imp ends up after teleporting. When close to the ground, the energy ball will move in a line. If the Imp is higher in the air, it will curve.
Defeating the Minotaur
The Minotaur is the level 1 Boss. He will begins at the side of the screen and builds up a charge. During this time he is invincible. After a few seconds, he will quickly charge to the other side of the screen. Jump over him and he will become stunned when he hit the other side. Attack him during this time.
Defeating the Mother Slime
The Mother Slime is the level 3 Boss. She basically only jumps and moves. When damaged, she will split into smaller pieces which are faster and more difficult to hit.
Fame points
Fame points can be used to purchase new colors for the interface, background songs, gravestone decorations, and characters. Everything besides the characters are purely cosmetic and do not affect game play. Save your fame points on new characters first, before spending them on cosmetics.
Stats
The following stats determine the performance of your character. Weapons and armors sold by the merchant will help increase some of these stats when equipped.
Attack: Shows how much damage you deal.
Defense: Determines how much damage you can take.
Luck: Limits how often enemies drop gold and items.
Reach: Relates to how big your weapon is. Higher reach weapons are safer to attack with.
Speed: Determines how fast your character moves.
Weapons
Weapon bonuses purchased from the merchant do not carry over when you use a new weapon. Buffs will be specific to that specific weapon when it is equipped.
Armour...