Mixing tech and magic can be a rough combination in a setting. There are a few settings that do it markedly well; Shadowrun from Catalyst Labs (and formerly FASA) is among a rare few that do it in an exceptional manner. Sometimes the mix is off-putting to players and GMs alike. It turns into a contest of “You got magic in my technology!” “No, you got technology in my magic!” In the end, perhaps it’s just not a good match for some game groups.
However, for those that want to try it, it can be done to great effect, but there have to be a few ground rules.
Magic and technology must be two great-tastes, together and inseparable. The magic and the technology need to be almost inseparable; but not necessarily to the point of having magi-tech (though that is a good solution). Maybe the magic is a fuel source for the mechanical devices, or maybe even a form of weird technology creates the magic fields that sorcerers and technomancers can manipulate.
The setting has to hold magic and technology in equal regard. If one is favored over the other, the players will gravitate toward the stronger option. They will view the weaker option as esoteric and quaint at best, and archaic and inferior at worst. Technology cannot be bolted on to a magic setting, nor can magic simply be bolted onto a technological setting; they must be blended.
When the setting incorporates both, the players can get into the setting better, the GM can run the game better, and the experience will be better for everyone involved!