Paris is considered to be a safe city compared to many others, but a god advice is always to pay good attention to your values and yourselves.
In the area around famous attractions there are quite some pick pockets, and that is also true for buses and packed metros. It is not advisable to walk alone in the darkness, at least not if you live a bit outside the inner city.
In some places you can find salesmen trying to sell you all kinds of articles at high prices. They do not need to be feared, but if you are not interested, simply walk by them.
This information is simply for you to take care… but, in general there are no problems, so your task is first of all simply to enjoy Paris and the wonderful atmosphere of the town.