Glad to hear you want to start using oly lifts in your training.
As far as when and how often to do them, it's all relative. If you've never tried them before, then you will really want to focus on executing the lift as correctly as possible. This might mean spending an entire training session just on the snatch or c&j as well as the assistance exercises for those movements. These include overhead squats, high pulls, etc.
If, on the other hand, you have some proficiency with the snatch and c&J then I would recommend the following pairing:
Snatch on the same day as but before deadlifts (and its other variations)
C&J on the same day but before before squats (and its other variations)
Hope that helps.