You need to be careful running simply lower fuel as this changes the balance of the car. I find that a dialed in set-up for the Lacetti on race fuel often goes oversteery once you simply take some of the weight out of the tank and off of the rear axle.
Best to redial in once fuel is removed to restore the high fuel position.
Try lowering the tire pressures aswell, this can sometimes offer more grip but only for a few laps. If in an open qualifying session (i.e. no superpole) try and make it so the tires are at their optimum temperature (around 90 degrees for most cars) on your third lap or second hotlap. Dont push the limit on the first hotlap and lock up/make mistakes as this ruins your momentum/ concentration and damages the tires, just get a feel for the car and hopefully on your second timed lap you'll be 'in the zone' and fully aware of the car balance/ grip levels which will let you hit your best lap time. With superpole it's a lot harder, you need to test what pressures get the tires to 90 degrees for your only timed lap beforehand and also learn what kind of outlap you need to do to achieve this, i.e. slow and smooth or hard and erratic.
Besides setup issues, there is sometimes a tendency to overdrive during qualifying (push too hard), thus throwing yourself out of the optimum racing line or having to brake where not otherwise necessary. Be sure to make a couple of 3-4 lap qualifying mock runs during practice to find where that edge is and drive the same way during the real thing.