Hi,
To develop effective Meta tags you firstly need to think about what you wish your site to rank for. Do some keyword research, utilising tools such as the Google keyword tool.
Once you have defined your keyword list, develop your content to incorporate a keyword density of around 2% (2 keywords for every 100 words of content).
Now it's time to think Meta!
The most important of these tags is the description tag. This tag lets the search engine know what the page is all about. So you should aim to use your most important, or high search volume terms at the beginning of this tag, and make sure these keywords are the ones you have used in your now keyword dense content. A good structure has been mentioned which I agree with:
Keyword 1, Keyword 2 | Company/Brand Name
Limit this tag to 64 characters, although I do believe that Google will now pick up to 75 Characters - anything longer won’t be read by the search engine after the character limit. IT IS IMPORTANT TO NOTE EACH AND EVERY PAGE ON THE SITE REQUIRED A UNIQUE, INDIVIDUAL TITLE TAG.
The next most important tag is indeed the description tag. This helps to let the search engine and the visitor know what the page they are looking at is about. It should be descriptive (matching the on page content), informative and use keywords from your research.
The keywords tag: Do not spend long with this, add a few keywords in but don't spend too long on it. As its worth as a ranking factor is little or none.
H1, H2 tags. These are basically the larger bolded text or headings (as in heading 1, heading 2). The h1 should contain your main keywords. H2 should be used to separate content and introduce a new section or paragraph, again using keywords but with more of an explanation about what is next on the page.
You should also consider looking into the geo tag, as Google is sure to place more relevance on this now and in the future as it continues on its path to deliver relevant search results to users.
Hope this helps.