Eh I prefer doubles, but do triples when warming up.
The parameters are going to be based on your overall weekly volume. If you have 2-3 snatches, your volume will be lower in each session than if you were to only have 1 session. This is definately a lift where you have to think in terms of movement and overall volume, because its useless to even break it down to leg day and upper body day since the lifts work the entire body.
If youre new to the lifts, you want to do them very often and with moderate volume to drill the form down. As far as knowing whether youre doing them correctly, well...get a coach or post some vids.

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Olympic Lifting Coach & Motion Specialist