Hi Cumbrian,
A few tips that might help out.
Let your telescope 'cool' for about a half hour or so before use
While your scope is outside 'cooling' try to dark adapt your eyes (this usually involves me sitting next to my scope and viewing the stars with the naked eye - don't look at the moon!!)
Start with your low power eyepiece (25mm) and try to get to M42, in the 'dagger' hanging off Orions belt
If Allan's focussing suggestions have helped you should see plenty of nebulosity
Now centre your EyePiece on the four stars at the centre of this 'cloud'
Then change to your 15mm EP - the nebulosity may look 'deeper' (tho' you won't see as much across the field of view) and the four stars should be easier to see - they should look further apart
If this has all gone well then go berserk and put the 6mm in - the stars will be easier to see again and the FOV will be so narrow that the nebulosity will only just be there.
Of course while you're doing all this you will have to 'nudge' your scope to keep everything in view, cap your EP's, re-focus, etc.
Above all - practice, my first few nights with an 8" Dob were awful, eventually you'll get that OOOHHHH!!! moment - mine was 47Tuc, in focus, on a clear, still night
and Saturn ANYTIME with your 15mm EP will blow you away
VAZ
PS. Find a pal in Brissy (there's lots on IIS) that can meet with you and 'show' you the ropes - this is probably the quickest way to be shown what you are doing right and wrong