just walk right in ask to speak to the owner, the manager or whom ever is in charge of property managment. ask them if they would be interested in letting you give them a bid, if they say yes which most will just because they want to see how competative there current landscaper is even if they are not planning on swiching services. if they say no we are all set then had him a bussiness card and tell him if he ever needs changes his mind to give you a call.
they like one on one contact it builds there trust in you and your company, be as friendly as you can be.....the first few places you go to you might be extremely nervious but stay in there once you do it a few times u will lossen up and flow more freely