About Players
Just as every GM has a style of running the game and of playing monsters and non-player characters, players have their own style too. You can shape them so that the game comes as close as possible to your vision, but you cannot really go against the natural temperament of the players. Few people can completely set aside their own personality, knowledge and interests, so a player always projects himself into the game (if only to a limited degree).
As a GM you must be able to read your players. It is not only about how they play their characters and how well, but how they behave in the group and what they expect.
Player Types
The following paragraphs describe some typical players, and any player may combine several of these types.
Passive Player
Especially a beginner, but even an experienced player, lets the others “lead” him by the hand. He waits for what you as the GM prepare for him or what the other players arrange. He joins in when his character's abilities are needed or when an action is required of him.
You must “fire up” such a player, otherwise the others will take over the whole game for him and he will never really get involved. For example, you can prepare the adventure so that the passive player's character is at the center of events - he receives / finds a mysterious item, as a priest or believer he receives a quest from a higher priest, he holds a noble title and so on.
Leading Player
This type of player is the natural leader of the party and the exact opposite of the passive player, whatever his character is. He will lead negotiations, handle the main tasks and decide the direction the others will go. He can be an asset, or he can push the others out of the action, especially passive players.
You will hardly steer a leading player into a role where he is equal to the others; it would go against his nature and he might not enjoy the game. Try to balance the game by occasionally giving the others a push - they find something, negotiate or arrange something, or take over the leading role themselves.
Natural Fighter
The natural fighter revels in combat, weapons, the combat system and similar things. Solving riddles or complicated diplomatic tasks bores him and he loses attention. As soon as it comes to the fray of battle, he takes up his role (and the dice) and throws himself at the enemies.
You will not change a natural fighter - after all, he enjoys the game (as long as there is fighting). If you have several such players, your adventure will probably be more action-packed and blood will flow freely. If you have only one, give him a fight now and then (at least once per session). Putting the player in a different role is not a solution either - if you do, he will probably be bored.
Born Mystic
The opposite of the Natural Fighter is a player who revels in more demanding fields, such as a player who always plays a wizard, priest, thief or another field with many options and combinations. Most of all such players love a combination of two or more different fields. This type of player is usually an asset to the game and there is no need to change anything about him.
If you want, you can let him try an uncomplicated character (purely combat-oriented), but he will probably return to his old ways - he will open more skills or try to gain special abilities later on.
Stats Hunter
These players try to improve their character as much as possible and have the highest numbers the rules allow. In the rules they usually also manage to find the most advantageous or most interesting combinations to gain better abilities. Naturally, they are also interested in the best possible items and equipment.
You can hardly forbid it; if they enjoy the stats, let them have them. The only change is that they will reach more demanding quests with more dangerous opponents sooner.
Rules Lawyer
From time to time almost everyone slips into this role, but a permanent Rules Lawyer is a real tough nut for the GM. For one thing, he usually knows all the rules (including the Bestiary) by heart, but above all he argues about every decision the GM makes. You must either rein in the Rules Lawyer (do not show your rolls, do not name the monsters, or use your own) or make him a GM.
Character Choice and Player Type
If a player picks a character that goes against his nature, he will be unhappy with it and will not enjoy the game. A “Natural Fighter” will hardly play a character focused purely on spellcasting or negotiation, while leading players most like to play wizards or other powerful characters. If you discover such a mismatch, talk to the player, “get rid” of the old character (a heroic death, leaving the group) and give him a new character that will better suit his playing style.
For some players it may be interesting to try a new style, for example when you start a new game with new characters. Nevertheless, players will hardly overcome their nature.