1.Keywords in title tag  :
As per HTML specifications it is not mandatory to write something in the 'title' tag. In case if you leave title tag empty then the title bar of  the browser will read as  “Untitled Document” or similar, for SEO purposes  it  is good to use 'title' tag.
The title tag must be short with in 6  to 7 words and the keyword must be near the beginning. Keyword in the title tag  is one of the most important places because what is written inside the 'title' tag shows in search results as your page title.  
Search engines (including Google).  Mostly display content of  the 'title' tag.
For example:
The title tag of the  home page for the http://see-seo-tips.blogspot.com can include  something like this:
'title' Search Engine Optimization Tips – go through these  useful interview tips to be successful in  interviews. '/title',
'title' Search Engine Optimization Tips - Everything  You Need to Know regarding interview tips '/title'
2.Keywords in URL : Keywords in URLs help a lot in getting better position in search engine  result pages.
Eg:-http://srihithas.com/webdesigning.html,  
 Where “webdesigning’” is the keyword phrase where we attempt to  rank well. But if we don't have the keywords in other parts of the document, we  don’t need to rely on having them in the URL.
The domain name and whole  URL plays an important role IN SEO process. The presumption is that if our web  site is about cows, you will have “cows”, “cow”, or “calf” as part of our domain  name. For instance, if our web site is mainly about cow milk , it is much better  to name your cow site “cow-milk.net” than “animal-milk.org”,
Because in  the first case we  have two major keywords in the URL, while in the second one  we have no more than one potential minor keyword.
Don’t be greedy when  hunting for keyword rich domain names. From search engine optimization point of  view it is better to have 5 keywords in the URL.
But if we imagine the  URL by using 5 potential keywords it will be long and difficult to memorize. So  we need to balance keywords in the URL and the site usability. So it is  advisable to use less than or equal to 3 keywords in the URL.
Directory  names and file names are also important. Often search engines will give  preference to pages that have a keyword in the file name.
For instance  http://ourdomain.com/interview-tips.html is not as good as http://tipsoninterview.com/interview-tips.html  but is certainly better than http://ourdomain.com/interview-guidence.html. The  advantage of using keywords in file names over keywords in URLs is that they are  easier to change, if you decide to move to another niche.
3.Keyword density in document text :
After we have chosen the keywords that describe our web site the next step is to  make our web site keyword-rich and to have good keyword density for  our  target keywords. Keyword density is a common measure of how relevant a page  is, the higher the keyword density, the more relevant to the search string a  page is. Recommended keyword density is 3-7% for the major 2 or 3 keywords and  1-2% for minor keywords. We can check keyword density by Keyword Density Checker  tools which are available freely.
If we make keyword stuffing there are  severe penalties including ban from the search engine because this is considered  an unethical practice that tries to manipulate search results.
4.Keyword stuffing :
Keyword density over 10% and above which are artificially inflated in a webpage  is regarded as Keyword stuffing and there is a risk of getting banned from  search engines.
5.Keywords in anchor text :
If you have keyword in the anchor text in a link from another web site, this is  regarded as getting a vote not only from this web site but also from your site  in general but about the keyword in particular. So it is good to have anchor  text for inbound links.
6:Keywords in headings (H1, H2, etc tags) :
Keyword in header tags counts a lot. But before placing ensure that the web page  has actual text about the particular keyword.
From literacy point of view  headings separate paragraphs into related subtopics. From seo point of view it  is good to have as many headings on a page as possible even though   it may be  pointless to have a heading after every paragraph, Especially if we have  keywords in the headings.
Even though there is no technical length limits  for the contents of h1, h2, h3,…. h5  tags.
We need to be wise with the length of headings; too long headings  are bad for page readability. Another issue we need to consider is how the  heading will be displayed. Heading 1 (h1),  means larger font size  in  this case it is recommendable to have less than 7-8 words in the heading,  otherwise it might spread on 2 or 3 lines, which is not good.
7.Keywords in the beginning of a document :Placing keywords in the beginning of the document also counts, however,  beginning of a document does not necessarily mean the first paragraph – for  instance if we use tables, the first paragraph of text might be in the second  half of the table.
8.Keywords in ALT TAGS :Search engine Spiders don't read images but they  read the  textual descriptions  in the 
 tags, so if you have images on your page, fill in the   tag with some keywords about them.
9.Keywords in metatags :
Placing keywords in metatags is important, especially for Google, Yahoo! and MSN  as they rely on them, so if you are optimizing for Google, Yahoo or MSN, fill  these tags properly. In any case, filling these tags properly will not do any  harm so better to have metatags in the page.
10.Keyword proximity : 
Keyword proximity measures how close the keywords are placed in the text. It is  best if they are placed immediately one after the other (e.g. “puppy food”),  with no other words between them. For instance, if you have “puppy” in the first  paragraph and “food” in the third paragraph, this also counts but not as much as  having the phrase “puppy food” without any other words in between. Keyword  proximity is applicable for keyword phrases that consist of 2 or more words.
11.Secondary keyword :
Optimizing for secondary keywords can be a golden mine because when everybody  else is optimizing for the most popular keywords, there will be less competition  (and probably more hits) for pages that are optimized for the minor words. For  instance, “web designing in Hyderabad” might have thousand times less hits than  “web designing” but if you are operating in Hyderabad, you will get less but  considerably better targeted traffic.
12.Keyword stemming : 
In English we have words that stem from the same root.
Example :- ( dog,  dogs, doggy)
(KISS, KISSES, KISSING)
(JOKE, JOKES, JOKEY, JOKER)
 If you have “JOKE” on your page, you will get hits for “JOKES” and “JOKER” as  well, but for other languages keywords stemming could be an issue because  different words that stem from the same root are considered as not related and  you might need to optimize for all of them.
13.Synonyms :
Synonyms are not taken into account when calculating rankings and relevancy in  languages other than English. Optimizing for synonyms of the target keywords, in  addition to the main keywords is good for those sites developed in English, for  which search engines are smart enough to use synonyms as well when ranking  sites.
14.Keyword Mistypes :
When searching for information using a particular keyword Spelling errors are  very frequent and if you know that your target keywords have popular  misspellings or alternative spellings.
 Examples for keyword mistypes
 (Christmas and Xmas) (Diwali and Dipawali)
 Targeting these misspelled keywords might get you some more traffic but  having spelling mistakes on your website does not make a good impression, So it  is better not to use these misspelled keywords in the content, but we can use  them or try misspelled keywords in metatags.
15. Keyword Dilution :
When webpage is optimized with an excessive amount of keywords, especially  unrelated ones, this will affect the performance of all the keywords and even  the major keywords will be lost or diluted in the text. So don’t target more  keywords in one single web page.
16. Keyword phrases :
Keyword phrases consisting of several words can be optimized in addition to  keywords, e.g. “Keyword Analysis”. It is best when the keyword phrases you  optimize are popular ones, so you can get a lot of exact matches of the search  string but sometimes it makes sense to optimize for 2 or 3 separate keywords  (“keyword” and “analysis”) than for one phrase that might occasionally get an  exact match.