The recommended approach is to remove the heatsink, clean up the existing gunk by using a cottonswab dipped in iso-propyl alcohol and place a small pea drop at the centre of the processor.
Once the heatsink is mounted, the pressure of the mount should spread it evenly across the processor.
This is how much I had applied for my i5-3470
Note that CoolerMaster recommends spreading the gel across the CPU evenly with the spreader but in my experience that causes more problems and it's easier to just put a drop and let the heatsink do the job.