Lawn maintainence while a property is up for sale is one of those things that everybody hates, no one knows who is supposed to do it, and is an all round pain in the butt.  One of the things I would do is hire a reputable lawn care company.  Fertilize the yard and kill the weeds.  If the homeowner will do this thats the best option but if you are property management you might get stuck doing it, so choose well.  Most banks and lenders wont do anything on a foreclosure unless forced to by codes or regulation enforcement.

Get a specialist in trees to do the trimming.  You dont want to kill that beautiful oak tree, do you?  An arborist is also a good choice for buyers to have the trees on the property inspected for disease and permenant damage.  Every little thing can make a buyer buy so it behooves you and your commission check to keep an eye out for possible problems.

I know that I cannot stand to go past a yard with a for sale sign on it and notice how shabby it looks.  If its in MY neighboorhood it can actually LOWER my property value.  Make a run around the block and get code enforcement out there if you see a home thats not up to snuff.  Every homeowner has to follow certain city, county, or state codes concerning property so do this and make the sale!!!!!!