Why couldn't you of just googled this? You can find an answer within minutes.
Anyway if you have no prior experience with with substance anywhere from 400-1000mg would be a good starting point. A lot of people do around 400mg for their first time. It's strongly user based some people do 1500mg there first time and feel nothing and others do 200mg and feel a lot. I would just say take 150mg (presuming they are the 150mg tablets) every 30-45 minutes until you feel a sweet spot.
[TABLE="class: ROATable mw-collapsible, width: 100%"]
[TR]
[TH="class: ROAHeader, colspan: 2, align: left"]
Oral[/TH]
[/TR]
[TR]
[TH="class: ROASubHeader, colspan: 2"]
Dosage[/TH]
[/TR]
[TR]
[TH="class: ROARowHeader, align: left"]
Bioavailability[/TH]
[TD]90%[/TD]
[/TR]
[TR]
[TH="class: ROARowHeader, align: left"]
Threshold[/TH]
[TD]50 - 150 mg[/TD]
[/TR]
[TR]
[TH="class: ROARowHeader, align: left"]
Light[/TH]
[TD]150 - 300 mg[/TD]
[/TR]
[TR]
[TH="class: ROARowHeader, align: left"]
Common[/TH]
[TD]300 - 600 mg[/TD]
[/TR]
[TR]
[TH="class: ROARowHeader, align: left"]
Strong[/TH]
[TD]600 - 900 mg[/TD]
[/TR]
[TR]
[TH="class: ROARowHeader, align: left"]
Heavy[/TH]
[TD]900 mg +[/TD]
[/TR]
[/TABLE]