Forget the blue apart from the first bit. The first couple of miles is pleasant undulating single track (which is repeated on the way back) after that it’s boring long fire road drag.
If you have newbies it all depends on their fitness.
If they are aren’t that fit then do the blue from the main car park to warm them up. Then ride up to Transmission (it’s a longish fire road climb or a shorter fire road climb followed by a rooty track depending on route), Accelerator and Nitrous.
If they are pretty fit then do the Black from the main car park and then link it with Transmission etc. There is nothing on the black that doesn’t either have a bail out or they couldn’t get off and walk.
Pretty much everything on the red and black could be ridden by a newbie if they take their time – we took a mate who was riding a ‘town hybrid’ down Transmission last year and he survived (we did worry the forks might detach on the way down as he’s a bit portly).
If they are fit take them up to Section 13 (it’s a pretty brutal climb up a washed out track) after that follow down to Special K and Brain Freeze. If not so fit take the road to the start of Special K.
This will give you an idea of where things are –
http://www.forestry.gov.uk/pdf/HamsterleyREDTrail.pdf/$FILE/HamsterleyREDTrail.pdf
http://www.forestry.gov.uk/pdf/HamsterleyBLACKTrail.pdf/$FILE/HamsterleyBLACKTrail.pdf