It is tricky to translate it into the world, beyond a sense in the back of my mind that the magic is not there as much. I only have a couple of Caster NPCs running around, and my players are not into playing often enough to add any to the mix. I have thought of adding more, to see how they play with things, but have not found the right story to pull such a character out of the aether. Sorry if it seems like I am being vague on the matter, but this is pretty much all I have on the subject of magic.
Sounds like you need to work on the other aspects of your world first. I find that be really getting into the who what why and whens of it all, you can find ways of running all manner of campaigns with whatever style, themes and flavour you wish.
[sblock]Have you mapped out the cosmology? Are there gods? Where do people go, if anywhere, when they die? History? If you have dungeons or ruins, who built them? In the case of ruins, what ruined them? Magical items? Do you have any? Who makes/made them? Where are they, the items and the makers, now? Are there other planes of existence? How do, if at all, people interact with them? What lives there and can they/do they visit?
With our current world, the third in our campaign, I started with a theme: 1001 Nights meets Ravenloft. Then I added an interesting seat of power for the local big cheese, added another smaller trading community, and then scattered some adventuring sites and terrain. Questions to how the ruler kept power were answered next, followed by threats and ambitions. Then it's other forces that threaten and so on.
While working on that, questions of magic would pop up so I'd make notes on a few ideas. As more pieces came together, magic and its role naturally found its place within the continuity of the world. In this case, drawing inspiration from Ravenlot's mists, magic is kept 'quiet' by The Sands, a mystical aspect that threatens spell casters who use magic while in the desert
(which is 80% of the campaign map at this time.) How it threatens is left to the DM, but its typically a Sam Raimi style vibe, where magic can produce unwanted
(and often horrible) side effects, typically in the form of the attention of monsters and dark forces.
With the previous world we have a totalitarian academic institution that controls magical innovation and research, which is referred to as SCIENCE. Long story short, excessive peer rivalry and an ingrained fear that magic
(i.e that which is not SCIENCE and cannot be trusted) causes mental instability
(which buys a ticket to a nightmarish Victorian-style mental hospital) means that 1st through to 3rd level SCIENCE is more widely accessible, at the cost of continued scrutiny, paperwork and faculty obligations. Beyond 3rd is 'experimental' and thus dangerous, obviously the work of con-men, charlatans and the mentally deviant. The in-game result is that magical ability comes with a lot of role play baggage that is intrinsic to the campaign setting, has worked very well, with all our players of magic user embracing the fun/spirit crushing bureaucracy. It also neatly avoids the problem of low level magic-marts and magical services because it is not acceptable for practitioners of SCIENCE to stoop so low as to meddle with the affair of the common people. Those that do are obviously deviants and showing signs of mental instability - cue the horrible Victorian mental health treatments.
So aye, who what why and when. Much easier to fill in the gaps when you have enough things to actually make gaps. [/sblock]