As the contact surfaces should already be as smooth as possible, all the TIM needs to do is fill the microscopic gaps. An even layer is the most important thing, second comes the layer being just thick enough to cover the grooves, but no more. Third is the care taken to avoid spills over the chip's edges.
So, apply evenly with a sharp-edged tool(voided credit card, knife), spread only as much as you have to to cover the laser-etched markings, and don't go over the edges. That's about it: even contact is priority #1, and you don't need a lot of it. My tube has lasted me four PCs, and is still running strong.
I usually start mine with a line across the chip, then spreading towards opposing corners, filling in the spots that don't have enough afterwards, then smoothing the whole thing out. It'll come to you as you do it, as long as you keep your brain thinking.