Be Proactive: I prefer what I call the “closed sandbox” style of gaming. The game-world is a place that lives and breaths, and it moves and it changes with or without your character’s input. World-shattering events are unfolding around you and your character’s backstories can and should plunge them into accomplishing actions, but those actions are ultimately up to you.
If you’re an adventurer, that means there’s something you want, some need that isn’t being filled by a life of chopping wood at the local lumber mill. While I can and will be providing plot hooks, I want you to be the ones who decide what adventures you go on, what style of game this turns out to be, and what goals your character is seeking.
Want to take up arms against a tyrannical king who’s also your brother and reclaim your rightful throne? Awesome! Want to start an adventuring company and raid dungeons for fun and profit? Also awesome! I won’t promise the path will be easy, but I want it to be yours. What’s your character’s motivation for adventuring? What are his long-term goals and what does he want out of life? Does your character dream of running an underground rum-running organization and using the proceeds to start his own kingdom? Congratulations, the players now have their own rum-running company and small nation, and the world and the game will adjust accordingly.
Be Careful: A game based on combat cannot be fun unless there was a chance of you dying. A game based on objective can’t be fun unless there’s a chance of you failing. A story based off of character choice can’t be engaging unless there’s actual consequences for that character’s choices. I won’t be pulling punches or holding back when it comes to combat, reaching your quest objectives, or exploring the consequences of your actions. You can die, you can fail, it’s more fun that way.
This means you should not rush into combats trusting everything you meet will be ‘balanced’ for you, nor trust that some secret will come to light to let you easily overcome insurmountable obstacles. Intel, pre-planning, and being clever are important to win the day. Likewise, henchmen and hired help are always a (smart) option, and can help ease the blow of PC death by giving you another character to play you’ve already rolled up, are familiar with, and who’s already invested in your party goals.
This also ties into the ‘be proactive’ point above: maybe you’ll need to consult sages and libraries to gather information, maybe you’ll have to do more sidequests to gain allies and abilities, or maybe you’ll need to hire some mercenaries. This is a sandbox game, so I’d much rather see how you solve the problem rather than how I can show you how to solve the problem.
Forget about Alignment: Too often it becomes a strait jacket. It gets in the way of having characters grow and change, and it gets in the way of playing your character the way you want to play them. If we absolutely need to know your alignment for a spell or something we’ll worry about it then.
Make your Character Likable: It may seem fun in theory to play the sociopathic, evil loner, but it rarely is much fun for anyone.
Keep Combat Quick: Nothing slows down a combat like spending several minutes debating which combat alignment best capitalizes the situation, and while I won’t be mean about this, I reserve the right to allow the monsters an extra turn if you spend too much time debating. As a rule of thumb, combats should be kept in character; you communicate with each other the way you would on the field, shouting orders to those who can hear you and making quick decisions as the battle unfolds. Unless you are telepathically linked, opponents can hear everything you say.
Remember the Details: Bringing all sorts of gear and finding uses for it, packing wagons up with food and water for long trips, planning the day in a place where just surviving can be a struggle; I know to some people these things are annoyances, but to me these are as much fun as anything else in the game. I love buying and maintaining vehicles and animals, planning expeditions, surviving in harsh terrain. We can ignore it all if you want, but to me caring for the details is what makes a world come alive, which makes a character come alive, which makes a game come alive.