Questions about Basic SEO
1. what is the limit for keywords for each page
2. what is the limit for title characters for each page
3. what is the limit for description characters for each page
4. does it important to use and links in content?
5. does it matter to name all photos on flickr and picasa accounts?
6. how important to update website on regular base
7. how important link exchange (tricks)

here are my answers...
1. For the numbers of keywords, there is what you call keyword density. It is the percentage of times a keyword appears on webpage compared to the total number of words on the page. Many SEO experts consider the optimum keyword density to be 1 to 3 percent.
2. not more than 10 words, or not more than 70 characters
3. For the description, Google cut off anything more than 155 characters so limit it to 25-30 words.
4. it is like putting emphasis on the keyword, telling that the word is important.
5. is it putting alt tags on images? It will help, since search engines cannot read images it is essential to use alt tags. Some says it also affect search engine rankings for the targeted keyword.
6. it depends on the site. If your objective is to entice people to come back to your website on a daily or weekly basis, then daily or weekly updates are likely to be beneficial.
7. Link exchange - Link exchanging is still one of the best ways to promote your websites. It is free and effective. It not only improves your website PageRank and link popularity, but improves its search engines ranking.