How Important is META to SEO

What is a META Tag?
Meta tags are embedded into the page's HTML and usually appears between<head>and</head>. The title, the Description, and the keywords are the most important components. The title is used to tell the search engine what the theme is for the page, the description describes the contents of the website, and the keywords indicate what keywords are used to describe your webpages.  
Meta tags equal to name cards of websites which allows users to know the theme of the site from search results, and this is critical for SEO. When the user input a keyword, what display on the search result page are the title and description. Let’s refer to the following picture:
Optimization result for META Tag
As Meta tag is an important factor that will have impacts on the effect of SEO, a rational and meticulous use of the title, description, and keywords will substantially boost the SEO ranking and user experience. A bio-chemical instrument company conducted META optimization to 20 webpages at the end of June, the following are the results:  
流量效果.png 排名效果.png
The picture on left indicated the traffic of the website for the whole year, and the one on right showed the proportion of the Top 10 keywords ranking in google. After optimization, the traffic and Top 10 keywords were improved by 81% and 6% respectively in July, and kept a straight 5-month increase thereafter.
How to optimize the META Tag
How to make the Meta tag friendly to search engine and benefit ranking?
1. Study the websites to learn the features and types of the product or service and conduct thorough analysis to accurately define the customer demand.
2. Pick out the most matched keywords and embedded them into the title and the description and put them at frontal position if possible.
3. Be aware of keywords stuffing when plan your keywords for the title and description, it will result in down-grade by search engine.
4. Make sure the contents of your webpage are in line with the description, and irrelevant contents shall never appear.
5. Create the description in terms of user demand, and highlight the features making them compelling for users. Language style shall be in line with the website features;   
6. Keep the characters of Meta tag in a reasonable length otherwise it cannot be completely showed in search result page.