Practice, practice, practice, Hip. Find as many traffic-free corners as you can, and take as many different lines as you can. For instance, try the good line--start wide and finish wide, smoothing the corner out as much as you can. Then try the "Cat 5" line--start on the inside, brake into the turn, then sprint like mad to get your speed up. Notice the difference.

But really, though, start slow with whatever you're comfortable with, then gradually increase the speed and lean angle as you gain confidence. In a crit, good cornering saves energy, and saving energy is key when you're sprinting 2-3 times a minute.