i'm still working on my consistency as well, but here's my method/tip:
work on 1 corner at a time. i set a target lap time to try to keep my times under (something reasonable, but challenging). then, pick only one corner on the circuit at a time and try that corner different ways. different braking points, turn-in points, gears, speeds, etc. See how that plays into your lap times.
tough to be consistent when you don't know what's best...
once i'm satisfied with my "ideal lap" on a certain circuit, i take at least 10-15 laps on it with my goal being consistency rather than speed. for example, if my average time is ~1:07 on a given track, i will try to stay within 1:06.5 to 1:07.5. What i find is that after several laps, i actually have to slow myself down in certain areas to hit that 1:07 mark, and that's how consistency yields speed.