In reply to Kirill:
As previously mentioned, keep the heels low. This can be mediated by either keeping you bum out or by maintaining good calf flexibility.
Its useful to note the shape of the hold you are smearing on as it can be milked for more purchase by changing the direction of force.
Always keep pressing the heels down when reaching up to the next hold to maintain the smear,
A note about keeping the bum out, this will reduce the hip/leg drive when you push up as your weight is not over your feet. If you need to smear in a roof then you may want to keep your hips close to the roof for the extra extension to reach things. Bum out is helpful but you may be missing a trick in the long run not keeping supple.