Welcome aboard, Romain. Nice to see another Frenchie around here.
The trouble with playing Trek in France is that usually it's viewed as "the crappy old series with the pointy-eared guy". Having faced the problem, I would recommend the following :
- As has been advised above, if you can, have your players watch a few episodes or movies that match what you intend to do in your games and are good examples of the specificity of Star Trek (i.e. not Star Wars with phasers and poor FX, for instance).
- Quickly present the universe, the various races, the technology and especially the balance of power and ethos of the various powers.
Both of those are usually enough for the players to have a good idea of the universe.
If you intend them to play as Maquis, it could also be useful to present the situation in more detail (especially the Cardassian and Bajorand situations), and if you can have them watch a few DS9 episodes.
GMing in Trek is not that different from GMing other RPGs, so the usual advices stand. There are a few tricky cases if your players are in a starship, but since that is not the case you should avoid those troubles.
"The main difference between Trekkies and Manchester United fans is that Trekkies never trashed a train carriage. So why are the Trekkies the social outcasts?"
Terry Pratchett