Hi, I'm brand new to this community, but I have a hubby who knows bikes, loves bikes and has a sportster.
A question first, though. Does the bike have a reserve switch on the fuel switch? If you do, just turn it to reserve if you run out and you can start it back up again.
If its 'bone dry' (his phrase, not mine) fill up the tank, give it a few twists of the throttle to get the gas to the carb and crank it up. Also, make sure the vent on the gas cap is open.
Hope that helps a bit