A few tips:
At the first corner:
brake just before the little uphill and just before there apperars to be skidmarks in the road. keep braking longer than you think, you should brake so long you almost come to a complete stop at apex. sliding just a little bit at apex helps aswell. get on the throttle early as the exit speed is vital here.
Eau rouge should be taken at full throttle, with as small wheel movements as possible. you dont want to hit the cerb on the right side but you should cut the cerb on the left side as much as possible (without hitting the cone on the first one and without hitting the black tarmac on the outside on the second one.
Brake quite early after the long kemmel straight (about just where the cerb on the left starts). try to start steering in while braking with a little trailbraking. go as tight as possible through the S and then take some height for the right hand turn that follows the S combination. that right hander should be taken at full throttle (very hard). I keep hitting the cone here.
Brake late at the sweeping right that follows (rivage). wait untill you have passed where the cerb at the left starts. trailbrake is important here. I used double apex, but you could stay on the inside all the way, whatever feels best for you. Try to take some height and carry as much speed as possible through the left hand turn that follows.
At the superfast left turn (pouhon) you should be able to trailbrake to the first apex, and actually go full throttle from BEFORE the first apex, all the way through the corner. this takes practice and I've not gotten it right yet either.
At les fagnes the braking point is just behind the shadow line in the road. go tight through the S combination and DONT HIT THE INNER CERB ON THE RIGHT. the left cerb can be driven over. aim for a late apex in the left corner, as the edge of the track on the exit is tight, and its sand there, so a wheel outside that outer cerb means a dead lap.
The right hand turn that follows dont require so much speed through, just focus on a clean entrance to it. Hit the throttle as soon as possible without sliding out, and keep it down all the way through stavelot and blanchimont, all the way up to bus stop.
At bus stop, the first right turn should be taken as tight as possible, while at the left turn you should'nt even hit the inner cerb at all, focus on your exit speed here, as a good throttle aplication can earn you as much as half a second alone.
AND.... practice, thats probably the best advice.