Search engine optimization is very important if you want to get traffic from search engines. Other fact is that 70% of web searches only look in the first page of the search list. So if you're not in the first page. You definitely going to miss many numbers of visitors to your website/blog
Here I will give you the top 10 seo mistakes that people made. Read this post not once but twice and don’t try but don’t do these mistakes again.
1. When targeting keywords use keywords that people may search. Do some researches before selecting keywords. Keywords can break or make your website.
2. Nowadays leaving . It not only works as keywords. But it's what the people see when your site appears in the search results page.
3. Flash might be attractive but flash website without html alternative you're no more. :( provide an html version of it. A search engine spider can't read flash so it can't index it.
5. seo maintenance is important. Don’t think that once you optimize your site, it is optimized forever. If you want to be successful you must look at the SEO in a regular basis.
6. Most people think that SEO is all about Meta keywords and
7. Using images for headlines is an attractive thing but when it comes to SEO you are ruining your web/blog in a long run. So try modifying them in a style sheet or this.
8. Ignoring keywords in URL's is something that many people do. But just think, if you have keywords in the URLs this gives you additional advantage over your competitors. Keywords in URLs are very important MSN and YAHOO. Google, their relative weight is high. So there are no worries having keywords in URLs.
9. We all know that having more backlinks are always better in SEO. So because of this web masters go to things like link farms, forum spamming etc. but the hard truth is you could end up getting your site banned. So what you need is quality backlinks.
10.when you've written an article do some look back and check whether you're lacking your keywords for your content or not.
I Also recommend you to read Top 5 Mistakes in SEO which is similar to this.