Here's a shot of the first third of the slightly inappropriately named Sweeper on Buttonwillow Raceway Park's west loop with a plethora of visual reference points. Since it is decreasing radius in the clockwise configuration that Sport Rider tests with, I use a double-apex approach with an early turn-in point, then thread between the dark square patch (just right of center) and the long patch laid down by the outside wheel tracks of the cars.
Walking the track is an excellent way to pick up reference points if that option is available. The level of detail you can see at a walking pace or kneeling down on the track is far greater than most riders notice in a weekend's worth of laps. By freeing yourself of the constant motion and distractions of keeping the bike on course at speed, you'll see the track in far better detail and more effectively create a map of points to chart your course through challenging sections. Note that the most beneficial time for a track walk is after you have enough experience riding the track to know where you need the reference points to do the most good.
Another technique for defining where your most essential points of reference are is mental visualization. Find a quiet area free of distractions, shut your eyes and envision several laps. This should include as much detail from all your senses as you can imagine: visual cues, what the engine sounds like, the inputs you make on the bike (like steering and shifting), bumps on the track, the timing of your movements, everything. There will be portions that are full of detail you can recall clearly, while other sections will be missing detail to the point where you feel lost. It's these points where you lack reference and need to fill in the blanks. Without reference points, you're basically riding blind.
The square patch (left of center frame) is my cue for my final turn-in point about 15-20 feet beyond, depending on my confidence in the front-end traction and steering response of the bike I'm riding that session. My vision is already scanning ahead to the apex point on the curbing near the top center of the photo for a late final apex that allows me to pick up the bike off the edge of the tire and accelerate off Sweeper into the entrance of the esses section. | 
The long patch from the car's outside wheel tracks continues through the middle of Sweeper, shown here. My cornering line crosses over to the left side of the long patch just at the lower edge of the photo; then I'm looking for the square patch that looks like a dot on a lower-case "i." Always have the center portion of your vision scanning (not stopping and fixating) at least one reference point ahead of the bike to keep your line smooth and stay ahead of where you and the bike are on the track. | 
Whenever possible, use reference points on the track surface itself, or in this case the curbing. Here the rubber laid down over the curbing by cars at Buttonwillow makes an excellent visual cue for my final apex. Don't, however, allow your vision to fixate here; instead be scanning ahead to the exit point or, better yet, the entrance to the next turn. |