I find that overlaying the throttle and the brake helps to get the car to turn in whilst not losing too much momentum, as Soyuz said, especially into the first corner. You also don't need to use the full braking power on at any point - you only need to go up to about 75% on the brakes at most. Smoothness is the most important quality here - attacking the track with aggressive steering/throttle inputs will usually just result in overheating the front tyres, causing excess understeer. I use the left stick for steering, L2 for braking and R2 for acceleration, and it seems to work pretty well.
As for how to specifically approach the lap, it's useful to watch the ghosts of course but for most of us it's unrealistic to expect to be close enough to them by the end of the track for them to be much use. Here's what I've been trying to do, just in case it's of any help to you. If not, just ignore the next paragraph.
The best way to start a lap I find is to run wide around the final corner and hug the outside of the track. I aim to cross the white line at the end of the kerbing at 65mph and the start-finish line at 85mph. Brake gradually, starting at the white line into turn one, and aim to hit the apex just after the cones on the inside at ~72mph. Prioritising exit speed you should be able to reach 78mph before turn 2. For turn 2 start braking at the marker board just after the line whilst turning into the corner. Aim to apex at 39/40mph and only power out once you don't quite need the car to be on full lock to get around the corner, if that makes sense Full lock seems to really hamper the car's acceleration a lot, so it's best avoided. Turn 3 only needs a slight touch on the brake and to ease off the accelerator, but the line is probably the hardest one to nail. For a good exit you want to just barely cut the grass on the inside and apex at ~58mph, and be doing 60 as you run wide onto the bit behind the kerb. With any luck you should be able to ease around turn 4 at 72mph, cutting over the kerb but obviously being wary of the cones. Stay towards the left of the track for turn 5 and brake lightly, no real markers here so it's difficult to nail but the line isn't so critical here. You don't need to hit the apex, but aim to be at 52/53mph around the apex and let the car drift wide to gather speed, but cut back in for the shortest route to the line.
Smoothness is definitely the key, so it may be useful to lower the steering sensitivity if you're like me and race with it on 7 normally. Oh, and turn the traction control off! It's annoying how it resets to 7 every time you quit GT Academy...
Anyway, I hope that helped, and if not, sorry for ranting! My best time so far is a 1:03.474. Equal seventh for DS3 users in the UK the last time I checked. Much better than I was expecting!
