Hi, I am not sure what you mean specifications, there is no rule for everything, I would recomment first to start commenting to your target blogs and wherever you get the chance engage with the blog owner/editor (respond to his comments and posts) and then after a while send your email by suggesting 2-3 relevant topics to their blog, this by far the best approach to guest posting...

Find a huge list of blogs you want to post on and send them request.

Very few will accept you but they will be worth the time if you pick the right ones with good PR.

Isn`t it obvious ? you should write an article closely related to the blog niche. The article should pe unique and of quality. Bloggers ask for articles of over 500 words but I`ve had some people ask for 250 words per article. Any other aspects about the article should be discussed with the blog owner before you actually start to work on the article.

Follow the writing style of the blog where you want to publish your guest post.
Pick a specific topic instead of covering multiple topics under one post.
include related images.
email your article to blog owner in text file (instead of MS Word).
attach the images in a separate file
Wait for the reply of blog owner

Guest blogging is done for link building and increasing traffic to your website..

If you are doing this then make sure you are sending quality and fresh article for higher approval rate and for viral benefit as well.

Thanks for the suggestions. Really worth a lot for Guest blogging starter like me.

Ok now, we have the unique content. but blog owner is not accepting link to your website. How to convince him?

People forgot to mention the most important thing here.... LINKS(Go for 1 link)

If you want to add a link to your website in the post... I would suggest you to add it in the author bio. Your post will look more natural. You can add quality site links like Wikipedia, etc. The blog owner won't mind such links.
Also if you find a word or a phrase in your article which is related to that Blog's other article, put this link to that keyword as well. Such internal linking will make your article look good and also will send a message to the owner that you have done a bit research about their blog.

Write articles from many angles. Be creative. Creative article ideas is the key to get the posts accepted. If you write a topic that's been covered over and over again, it'l unlikely it'll find a quality site to publish.

Guest post rules:
1.Make article with atleast 300 words
2.No copying content from other sites
3.No spamming of your own website/product
4.Dont put unnecessary links in the article

Usually, if you are going to do guest blogging, you should coordinate and ask the details (guest blogging rules and regulations) to the site owner. There are no specific rules but consider and expect some general ones like quality content, 2 links to the author box only, no selling of products/services within the content, no duplicate content, and so on.

Do I need to contact the website owner if submit form is provided?

How do I find B list blog?

Thanks again

Just find blogs with similar articles (the same topic or very related) and be sure that they rank high for the keyword you want to rank for! Then, just contact the webmaster and be as polite as you can!