The way i ensure this is to put all the wort from the fermenter into the keg.
I use a tap on my fermenter and let the wort run into the keg, when it gets quite low the wort has become a bit cloudy with the sediment in the base mixing slightly. If you stick all the wort in, including some of what is normally left behind you are also allowing a small portion of the yeast over to the keg to help prime.
its also means you dont have to worry about putting a spoonful of sediment in. less work = more beer time.