One of the most common ways for tourists to reach Devka beach or Daman is through Vapi. Shared taxis(in which the fare is distributed among the passengers) are available from Vapi railway station. But one point of advice is that these taxi drivers pack their car to the hilt to maximise their fares. Thus it could be an uncomfortable drive which takes around 30-45 minutes. Also they drive quite irrationally and people not used to the driving in India can have a nerve-wracking time :-)
Do not go for the shared option. It will cost a bit more, but atleast you'll have a better ride.