The trail building at GT never stops. The climb from The Hub (at the bottom) to Buzzards nest (the top carpark, a couple of miles in) is now all off-road and great fun – yes, climbing can be fun!
From there, you should mix + match the red + blue sections. Black's still loooong and 'out there' – you won't meet anyone – and round Buzzard it's busy on weekend afternoons. But get up to Spooky either on red or poofing-out straight up Anderson Road (avoids 2 fairly meaty climbs and one fun descent) and you're on the rollercoaster. There's at least 3 top-bottom routes from the top of Spooky to the Hub, each with loads of variations.
Study the map (which has improved too!) and just go round and round.
But also do Inners, it's amazing – a proper Mountain Bike track. 5 miles climbing to start with mind. But then there's the down… Oh, yes.
Maps:
http://www.thehubintheforest.co.uk/Downloads/7stanesglentressinnerleithen.pdf
Cheers, al.