I've always done it in one sentence as did my instructor. Don't forget you are asking the station for a service, it's your decision on what type of service you require, the station can always refuse a traffic service for example if they are too busy at that time. If you ask them, it saves time on the radio when they come back to you asking what type of service you require.
Hope that helps.
Alex
Edit: I've heard people just say their callsign on the initial call and for a service and transit at the end on their full message.
Last edited by Aspiring Pilot Alex; 27th Jul 2012 at 00:25.