Meta Tags are useful in SEO

The Meta Tags are not visible when someone visit to your site ,it is read by search engine and decides where your site place in search result page. Most important Meta tags are title, keyword and description tags. A search engine see the relevancy of Meta tags by looking at the keywords used them and looks the relevancy of keywords used with content of the page.
Every search engine uses its own unique algorithm to index the websites. All major search engines keep updating their search algorithms quite frequently to give their searchers the best searching experience. Your website place in search result according to calculation of algorithm it follows. These algorithms are not changing everyday but are evolving into more intelligent and accurate. Yet, the major focus is on the Meta tags of the site.

The Title Tag
Title tag is the first thing shown on a web page and this is visible to both your visitor and most importantly to the search engine. The title is the most important Meta tag of your website. That's why it has to be given the utmost importance while search engine optimization is the consideration.
This tag should include the most relevant keyword about your website. If the most relevant keywords are used in here, your web site will sure get a boost in a search.
It is not desirable to use company name in title tag. Because, nobody usually searches for a company name. The perfect title tags should be something between 10-70 characters. It is not so that one can not put a longer title but the search engine would ignore the longer part of the title.
The Title tag should be written for the visitors first and the search engines second. This should be such as to motivate a click and obviously to favor the search engine indexing too. Different title tags should be assigned to each page of your website containing its own keywords that relate to that specific page.

Keywords Tag
The most heavily sought technique in Search Engine Optimization process is Keyword optimization. But at the same time if keywords are too often repeated, chances are that the site gets marked out as ""spam"". However, if your target keyword are not included enough, its ranking will not be optimized. So, with present algorithms which are really smart and intelligent include only those relevant keywords you want to target and make sure that these are included in the contents too.
Use variations of a keyword like watch, watches, wrist watch etc. They are slightly changed keywords and yet don't render any feeling to the search engine for their being repeated in the tag.
Geographical information (name of the country, city or place) may be used in the keywords. Sometimes it plays a great role when a search is made for a location based business. Or, even brand names, model name of a product can be used in this tag. That also helps when a search is made for a specific product model or brand.
Write your Alt tags of the images and the text links being used in the page such that it includes at least one keyword from the keyword tag. But, remember the same should look just relevant with the image or the hyper link for which it has been written.
The content should have included all of your keywords. The aggregate keyword density (all the keywords used in keyword tag) should be between 20% to 30% but not less than 5% to the best optimized results. However, Density for a single keyword should not be less than 2% and higher than 6%. The best is about 5% with the major keywords and 2% with subsequent keywords.
The Meta tags should be fine tuned with the contents and a good relevance is brought about between themselves with a perfect balance between the target audience and the search engines.
These Meta tags have been used really very un-carefully by the spammers, if we commit to use them methodically with the due respect, I hope, we should be able to create ever increasing web traffic on our sites.

Description tag
The description tag should be written in a way that it describes your site in one or two sentences. It should be short and clear that your visitors get a close idea about your site by reading this in a short time.
The description tag should be 100 to 200 characters long. The Meta description tag also has a great role in the SEO of your page. This tag displays the information at a search engine result page (SERP) after a search is performed by a user. So, this should be such as this puts the concise summary of your page. Most search engines truncate longer Description. Remember this while writing this tag. Remember that the Meta Description Tag of a web page must not look just a bunch of keywords, but should contain an informative and concise summary of your web page.
Same as above every page should have a different description tag in accordance with the contents it holds. This tag has quite some effect on the ranking of your site in Search Engine results. The Search Engine will read your description tag and will check if the keywords or search terms match your title tag and content of your web site. My suggestion is to take the first sentence or two of the contents from your web page and use that for the Meta description content. Include the most relevant sentences matching with the page contents in description tag instead of stuffing the tag with more keywords