I would recommend taking 15-20mg orally for your first time as there is really no point to snorting due to your body typically being able to absorb more of the drug by simply swallowing it. The only benefit to snorting would be a faster onset, however the duration of the high is typically shortened.
If you are dead set on snorting I still recommend around 15-20mg just to get a feel for the drug and take more if needed.