There are a number of different meta tags - The main three you are worrying about for search engine optimization are:
Before you setup your meta tags with keywords you need to figure out what search phrase you are targeting. The major one you want to target in this case is "real estate". The idea is you want to come up #1 or at least on the first page of whatever search phrase you are targeting. For most of us kicking out Realtor.Com, Yahoo, MSN, RealEstate.Com and Newsweek for top position is a little beyond our powers. So we get more specific. What geographical area are we dealing with? If it is a county that is your region of choice you would specify the county. A city? Use the city name. A region? Use the region title and then put the words real estate after it.
My target market is Cambria, the town where I live and work so we will use that as an example. If you don't want to use "Cambria real estate" you can use, "Cambria homes for sale" or "Cambria condos" etc. My preference is real estate.
A great way to find related keywords is the keyword tool built into the Google adwords. If you have a Google adwords account just log in, click on tools at the top, then click on keyword tool. Enter a phrase like "Cambria real estate" then hit "get more keywords". And voila you have a list of related keywords that you can use. This will come in more handy as we go on.
The Title Tag is the most important meta tag to setup. Each page on your website should have a slightly different title, though you can use your key phrase if you so choose e.g. "Cambria Real Estate". For your home page or main site page use your primary search target phrase plus another major related keyword.
To get another major related keyword use the Google adwords tool to find related keywords to "real estate". When I just did it the top 3 were "real estate listings" "real estate agents" and "real estate agent". So a great title to a website would be "Cambria Real Estate Listings" This has your key phrase target and a strong related keyword modifier on it. It's tight and straight to the point which is what you want. If you want to hit multiple key phrases do it with a different page and title it accordingly.
The Description Tag is the second most important meta tag. Each page should have a slightly modified description for premium optimization. Around 20 words is good for the description. The tighter you can get everything the better. You want to target exactly what you want to rank and get up there. Get keywords from the Google adwords tool mentioned above and make sure you use the words you put in the description and title tags in the body of your page. If your site is about listings talk about listings on the page.
Some hot real estate keywords are: listings, agents, agent, listing, broker, residential, brokers, mls, agency, era, property, homes, commercial, find, sales, etc. Sprinkle these words into your description in a concise manor not repeating yourself. A good description might look something like this. "Find Cambria real estate listings and homes for sale. Search the MLS for commercial investment property and featured properties from our agency." This includes many hot real estate keywords in it. Just make sure to elaborate a little or at least mention these words in your main body to maintain emphasis.
The Keywords Tag is least important though if done right can help boost your search results. In listing your keywords make sure you include the words in the body of your page. A good thing to do is start by using the keywords from your meta title and meta description. A keywords tag for the page I have been creating might look something like this "Cambria, real estate, listings, find, homes for sale, search, mls, commercial, investment, property, properties, agency"
There is no exact science to it and no one has all the answers as these things change frequently. This is a basic outline of what has worked for me so far. Any additions in the comments are welcomed as I am free to always learn more.
Hope this helps and good luck!