Dungeons and Dragons
Players fun is your fun. Dungeon master is the enabler, players are the heroes.
Don't overplan. Planning is required but don't expect the heroes to follow your lead bindly.
Communicate expectations to players. How much puzzles, how much battles, what is the ratio.
House rules are fine. If there is a conflict with the rules, make a house rule for the session and resolve it later.
Encourage creative thinking. When one figures something on the fly, try to support it. If it's close to impossible, make them roll 20 on d20.
Create an interesting past for your character. Most interesting characters are the ones which background doesn't match what they do now. It will also help driving hero's decision making. But be brief about explaining it to others and reveal more as things go forward.
# boring Soldier => Fighter Thief => Rogue Noble => Paladin Scholar => Mage # interesting Noble => Rogue Thief => Paladin Soldier => Mage Scholar => Fighter