Sad to say, I have been guilty of breaking this one cardinal rule of role playing, but in my defence I will say it was done out of pure ignorance, and the fact I was a DM virgin ... plus I had a tendency to want my players to really enjoy my games, and before you know it, you yourself are being swept along on a coaster roller ride of sheer magic, mayhem and money!
"Gold". Mention that word around any role playing table and see the avarice glow appear in your players' eyes, that is, unless you mention the 'P' word: platinum - then your players would sell their mother (rp mother, I hasten to add) to get their filthy, grubby paws on such loot.
The only thing that comes close to this is the mention of tea, coffee and biscuits, then something similar occurs (and I don't mean to brag here, but apparently, I do make a pretty mean cup of tea!).
Gold is the root of all rp evil. It corrupts, it cajoles, it confuses and it complicates. Give too much and it causes apathy, give to little and it causes unrest and rebellion. Oh, and do not do as I had done when starting out; realising my mistake then introducing extortionate pricing for armour repairs, spell components (although, sometimes this can be justified, I mean, powdered dragon testicle should be hellishly expensive - think of the poor buggers who had to get it to begin with, and how!), board and lodging ... or, even worse, have the party robbed during the night.
Yes, I know. Shameful tactics and I am guilty of them. So don't do as I do, etc, etc.
Take into account the locality of your planned venture, the goal, the NPCs involved and those who could possibly be involved, possible encounters - and I hate/loathe/detest random encounter tables. Such bollocks! If you are the lazy-bastard type of DM, then go knock yourself out with the random encounter table, but if you have an ounce of pride in what you are doing and the responsibility you carry as a DM, then you should plan out the possible encounters beforehand according to terrain type, season, population of the given area, time of day/night, etc. At least this way, your encounters will make sense and feel natural and not disrupt the flow (and feel) of the game session.
Trust me, on the rare times I have been a player, there have been things that made no logical sense to me and brought me up cold in my enjoyment of role playing by having my mind ask question-after-question relating to the oddness of an encounter. Killing that band of giant spiders on the road leading out of the local village and looting their messed up corpses of 200 gold, one bag of gems, a magical sword that speaks with a voice like Julian Clary and six potions of uber healing is not a good start.
Rewards should be in scale of the danger and difficulty of the encounter - sometimes.
Why 'sometimes'? Sometimes is a nice reminder to the players that often an encounter is all about survival and nothing more. If the players get it into their heads that all NPCs they meet, or mobs they encounter are literally walking treasure chests then the game will quickly become a slaughter fest for all the wrong reasons.
***A poor old woman, stooped over and aged, carrying a faggot of wood on her back, gathered after many terrifying hours near the forest's edge, relieved to be back on the footpath back to her home village. But what is this she spies? Ahead approaches a small band of travellers. Fear fills her being. Adventurers no less, should her aged eyes be true.
She sighs in relief.
The old woman and the adventurers approach on the footpath, the gap closing between them. As the old women looks up and smiles, shuffling to one side to allow the brave, young adventurers past, a yell rends the air as the group turn on the stricken old woman.
It is over in seconds - well, two rounds if you really want to know - and the party search the hacked body of the old woman.
"Hooray!" yells the fighter, "A bag containing nearly 300 gold!"
"And look at this," remarks the wizard, "a staff of Never Ending Missiles!"
"Oh, oh, oh!" the thief of the group is dancing on the spot with excitement. The others turn and look at her with enquiring looks. Carefully the thief slips the Ring of Eternal Invisibility into her pocket.
"Oh, blast!" exclaims the thief rather dramatically, "I thought I'd seen a nice dagger, but it's only a Knife of +4 Fire Damage ... oh well."
Magic is a different beast altogether. For me, I have learned that to wield it willy-nilly in a game just ruins its impact and awe. If every dog and its master is throwing spells left, right and centre, then what should be an amazing - and sometimes terrifying thing - sight to behold, and be respected as such, becomes the norm, just like eating, drinking and sleeping.
I would rather run a game where the use of magic is limited to a very few powerful individuals, or to a very small minority within the game world - including your player characters. Hopefully this should highlight the fact that they are special within the game world and therefore regarded with awe, fear, hate and respect, as is the fighter/knight/barbarian who is visibly equipped for battle, compared to the normal folk with whom they would encounter.
Remember, a game world is unlike the MMOs we play - your players are meant to be heroes, maybe not right off the bat, but eventually they will become elevated above the normal standard of game world person by sheer dint of their travelling, fighting and experience. So you will not and should not have players enter a hamlet, village, town or city and see every other person to be a warrior/thief/wizard/ranger/cleric. It just would not happen. By the same token, your player characters should be exposed to the reactions of folks who have most likely, never seen their ilk before, and as such, should have a whole host of reactions played out accordingly.
This is the one main reason why MMOs will never and SHOULD NEVER replace traditional pencil and paper role playing games. Players can be individual, unique and diverse - whereas in an MMO, no matter what you choose to play, you do so with the knowledge that your so-called 'character' is just one of thousands of others in that same class, and most likely has a thousand 'twins' running about the place.
So magic should be the exception and not the rule within your game world. Never make it easy, either. I know D&D had an option for spell components to be used in spell casting and this would slow down the actual act of casting for magic users. I also know that as a DM, I never enforced such a game mechanic, mainly due to the fact my players disliked it, plus I didn't wish to slow down game events due to a wizard having to hunt through his pouches for the components and then combine his/her diced mushrooms, sweetcorn and pineapple in order to cast his pizza spell - ok, silly example, but I think you know what I mean.
But leaving out such game mechanics does not equate to easy casting. Just adjust things logically to ensure the balance is maintained and that magic users do not appear to have things easy. Saying that, I do feel they earn their spells, what with having to run about in nothing more than a mere nightdress to begin with, and being solely dependant on their armoured companions to keep them in one piece.
***Magic user: 'Help! I'm about to die!'
Bugbear, mouth drooling and eyes full of hunger, advances on the flimsily robed mage.
Warrior smashes his sword down on the hulking head of a second Bugbear, 'Use your magic!'
Magic user, scrambling for the nearest tree, robe hem pulled to the knees, 'I did, but I don't think it liked my Dancing Lights!'
Rogue, from above: 'Bugger off and find your own tree!'
So it is your role as DM to impress upon the players how amazingly wonderful and unique magic is, not only for the ones choosing to embrace and use it, but more so for those witnessing it.
Last of all, mayhem. Controlled chaos, if you will, with YOU, the DM, being the control.
I shall keep this brief; all out bar room brawls can be fun and a good form of light relief within a game, but keep as such. Limit to rare occasions, DO NOT make it the norm. You will attract the odd player who is hell-bent of causing as much havoc within a hamlet/village/town and city as they can. This will range from thievery across the board, acts of vandalism, cruelty and violence.
Don't take the approach of, 'You can't do that!', as it will only make you look like big brother spoiling their fun. But don't forget, you have Militia and the Watch to fall back on, not to mention the other player characters. Clamp down on such renegade characters, but do so within the confines of the game world. Should they escape the law, then there are always bounty hunters who can be called upon, and word will soon spread regarding your party fugitive.
In all likelihood, this kind of behaviour will stem from a new player introduced to the group who doesn't give a shit about rp, and sees it as a chance to screw things up. It is doubtful they will return after one session ... but you never know?