In WordPress the first thing you need to do is get rid of default permalink structure via Options > Permalink.
WordPress gives you complete control over how you want to customize your permalinks.

Having rejected the default structure you have three other options left:

Date and name based (Its way to long for my taste)
Numeric (Not really my thing, it look way to complicated for the visitor)
Custom (Just what we are looking for)

So you are going to enter custom structure tags in the Custom field.

We are looking for shorter URLs, so the only thing you are going to enter is /%postname%/

This gives us the shortest possible permalink structure: http://domain.com/post-name/

On the same page, there is another optional field named Category base. And while you are at it, you are going to make use of it too. You are going to enter a short word to replace the word category that is attached to your category URLs. Let us enter /tag here (
or anything else that is shorter than the word category)

Long Titles Short Permalinks

As opposed to short permalinks, your post titles need to be fairly long, because titles are the first thing searchers see when your posts appear in Google search results. So, a title should summarize the whole post in at least six or seven words. Although we know the importance of titles, we do not want the titles to stretch our permalinks to fill up the whole address bar!

Luckily, when on Write Post page, you can make use of Post Slug sub-panel, located on the right side of your Write Post panel, and add custom permalinks for every post!

For example if your title reads /%Learn the art of blogging%/ you can enter /%learn-to-blog%( in Post Slug. You leave out the unimportant words and keep the main key words.

Happy Tweaking!