I found that using latex surgical gloves is the easiest way than the plastic bag, that way I
know I don't get any oil on the heatsink or cpu. They also work great when eating chicken wings with extra hot sauce

.
As for the paste (I always use AS3), about the best I can do is with a razor blade at 45º angle. My problem is after 3 pots of coffee my hands get shaking a bit so an actual "even" layer is impossible

.
Mike