The key is to provide pertinent information to the type of unit and service you are requesting.
An A/G operator is not interested in much info, just your reg, type, and where you're inbound from. It is, however, good Airmanship to include more info for the benefit of other aircraft listening on the frequency. Be aware that some A/G operators try to offer more of a service than they are supposed to - I've had more than one 'heated exchange' with them after they've tried to issue instructions!
AFISO's and ATCO's need more info. If you are joining they (in theory at least) need to know where you are coming from so that they can pass traffic information to other aircraft participating in the Flight Information Service. This means that at least they will need to know which direction you are arriving from - current position is of course the way to do this.
For enroute Flight Information / ATZ Transit / CTR transit they will need to know your current position and any salient turning points that will affect their traffic ie. any turning points in or close to their zone, and the next turning point after you have left the area. This means that they have the full picture of where you are going.
"Luton Appraoch Good Afternoon G-ABCD for Zone Transit"
"G-ABCD, Luton, pass your message"
"G-ABCD a Cherokee, Biggin to Cranfield routing Brookmans Park, your overhead to Woburn, overhead Brookmans Park 2400ft on 1011 request VFR zone transit".
Another thing that I personally do often when talking to an airfield for enroute Flight Information is I say 'will remain clear of your zone' - I'm basically trying to convey the message 'I know what I'm up to and I'm not going to bother you much'. Might be useful to the ATCO/AFISO or maybe I'm just clogging the R/T - dunno - any AFISOs/ATCOs out there can comment?
[This message has been edited by foghorn (edited 15 March 2001).]