It is simple- dilute cells two-fold by serial dilution and culture cells. These cells exhibit slow growth in the beginning due to dilution.

I'm not sure if you mean that you are having trouble getting single cells vs clumps or if you cannot get them to grow after dilution, so here's my advice on both:

A trick I have used for another cell line that does not grow well in single cell conditions is to condition media with the parental cells. Some cells are very reliant on growth factors and other signals from neighboring cells that may take a long time to accumulate. 

To make sure that MCF-7 cells resuspend well as single cells, I have found that it is best to thoroughly trypsinize and resuspend for several passages before you actually need them to be single cells. Also, I pipet up and down with the tip placed against the culture surface to force the cells to break apart a bit more. 

Thanks very much for your information. do you have some literature about that How to trick single cell grow up well??