Permanent Link or Permalink as we popularly know it as are the permanent url structure of your blog post, categories mainly.
Wordpress has a default url structure as :
http://yourwebsite.com/?p=N
This form of url structure is not only ugly but not human readable as well. This is quoted on on wordpress.com too. So what do you do to change it’s structure and make it more search engine friendly ?

If you are on the wordpress blog it’s very easy to change the permalink structure. You can follow these steps in order to make changes:
WP Dashboard > Settings > Permalinks
Once you are there you just need to choose any of the 3 options which fits to your needs. But when you really want your blog to be search engine friendly and be able to get indexed faster you should use custom structure.
There are 3 main custom structures that are popular in the blogosphere.
1) /%postname% -
This is considered as the most useful permalink structure in the world of SEO. So the url of your blogpost would be like:
http://YourBlog.com/new_post
This type of format is not recommend by WordPress, they have stated the following:
For performance reasons, it is not a good idea to start your permalink structure with the category, tag, author, or postname fields. The reason is that these are text fields, and using them at the beginning of your permalink structure it takes more time for WordPress to distinguish your Post URLs from Page URLs (which always use the text “page slug” as the URL), and to compensate, WordPress stores a lot of extra information in its database (so much that sites with lots of Pages have experienced difficulties). So, it is best to start your permalink structure with a numeric field, such as the year or post ID.
Apart from that the only other known disadvantage is that youe blog posts will never be featured on Google News, since they need atleast 3 digit of numbers in the post url. If you don’t care about that it should be just fine. Cos I don’t.
But all said and done this is still one of the most popular choices while choosing permalink and iBlogMaster.com also uses the same structure.
2) /%post_id%-%postname% -
This is the second best form of permalink I’d recommend you. It has the post id in it. So it should be no problem for Google news to index your blog post.
3) /%category%/%postname%/ -
This is very useful if your blog is properly categorized. You have to remember that not every post can fit into a certain category. So if your blog is something related to a specific subject and has appropriate categories then go for it. But many blog owners are migrating from this type of structure for a better one.
If you are a blogger who is really worried about SEO then I would definitely recommend the first option.
You can also use a trailing slash at the end like this: /%postname%/ but it looks prettier without it.
Do share your experiences in here. I would definitely love to hear from you guys.