Tips: Keyword Length Best Practices

I've got a couple of questions from my client:

Do you mind to repeat for me: how many keywords I have to put for each page on the web?
You also mentioned that you may have some information about the statistics which words are most demanded.

How many Keywords should I target on each page?

Get tips with keyword best practices which help search engines find the content on your web pages from

• official website of the U.S. Government
  

Site Architecture for Search Optimization - Webcontent.gov - Guide to Managing U.S. Government Websites
http://www.usa.gov/webcontent/technology/search/optimization/sitearchitecture.shtml

• the World Wide Web Consortium
  

Provide keywords and descriptions
Some indexing engines look for META elements that define a comma-separated list of keywords/phrases, or that give a short description. Search engines may present these keywords as the result of a search. The value of the name attribute sought by a search engine is not defined by this specification. Consider these examples,

http://www.w3.org/TR/html401/appendix/notes.html#recs

• the HiSoftware Inc.
  

1- Keyword meta tag validation
One of the most important items in proper search engine indexing is the proper use of meta keywords. The checkpoints listed in this section for keyword validation assure that you are using keywords and that your usage does not break any key usage policies.

1.1 Validate Minimum Keywords Length
Your keywords meta tag should not be less then 200 Characters. When you use less then 200 Characters you are most likely not taking advantage of a search engines indexing capabilities.

1.2 Validate Maximum Keywords Length
Your keywords meta tag should not exceed 1055 Characters. When you exceed 1055 Characters some search engines may consider that you are trying to spam the engine. Additionally if the search engine mechanism uses keywords to index your page properly, you may be decreasing the accuracy of the search.

http://www.hisoftware.com/cc/searchability.htm

• Danny Sullivan: Search Engine Placement Tips› › › Webmasters

http://searchenginewatch.com/showPage.html?page=2168021

How to get information about the statistics which words are most demanded?

Google Ad Words provides a helpful keyword suggestion tool to guide web masters beyond the obvious choices of the product and services. Choose keywords, which are words or phrases related to your business. Go to: "Get keyword ideas" on Google page:
https://adwords.google.com/select/

For example, search a word "health" gave me 200 more specific keywords - sorted by relevance

health insurance, health, health care, natural health, health supplements, aetna health, dental health, group health, women's health, department of health, vitamins health, medical health, herbs health, vitamin health, womens health, mental health, health issues, health and fitness, health department, herbal health, health food, health articles, nutrition health, health information, united health care, mens health, united health, health remedies, discovery health, health prevention, men's health, health education, health magazine, oxford health, home remedies health, world health organization, calcium health, health net, cardinal health, health partners, health and human services, health questions, health and wellness, department of health and human services, home health care, health policy, health news, diabetes health, health savings account, public health, health com, health plans, dog health, health alliance, first health
health food stores, universal health care, memorial health, spectrum health, health savings accounts, national institute of health, health medicine, health plus, general hospital, kids health, health coverage, individual health insurance, health clubs, health south, cat health, sexual health, health cures, health article, mass health, assurant health, united health group, health food store, discovery health channel, doctors health, medco health, teen health, health cure, pet health, health insurance quotes, health problems, national institutes of health, mens health magazine, ohio health, oxford health plans, environmental health, allied health, health remedy, heart health, home remedies, texas department of health, oxford health insurance, health disease, health cancer, women health, ohio department of health, health insurance plans, florida department of health, sport and health, health secrets, affordable health insurance, health clinics, holistic health, health statistics, health foods, health promotion, baptist health, health insurance companies, denver health, health careers, men's health magazine, hospital health, banner health, department of public health, global health, health products, student health insurance, health facts, department of health services, health supplement, animal health, women's health magazine, health assessment, sutter health, group health insurance, health spa, children's health, aetna health insurance, health care insurance, health research, uw health, health community, national center for health statistics, blue cross, tufts health plan, alternative health, public health service, good health, health tips, us department of health, providence health, group health cooperative, harvard school of public health, health care costs, trinity health, united behavioral health, safety health, health resources, partners in health, health programs, ppo health, health psychology, mental health association, cigna health, health hmo, tufts health, oxford health plan, board of health, child health plus, health disparities, health fitness, chemical health, coventry health, memorial hospital, national health care, health care reform, national institute of mental health, cheap health insurance, childrens health, patients health, independent health, department of mental health, health administration, eye health, indian health service, new york state department of health, national health, dept of health, health insurance quote, public health jobs, health concerns, health clinic, occupational health, health inspector, physician health, basic health, metro healt, osha health, prostate health, california department of health, health report, child health, american health