For WordPress tags, default is fine but when it comes to categories and when you have a lot of categories in your blog then for selecting any category you have to scroll down and look after it but now by using a WordPress plugin you can make it simple. It filters your blog’s categories as soon you type a few beginning words of the category you like to use in your post and shows you the related categories, you simply click your category and that’s all. Just like Google and Facebook (now Twitter also) search suggestions.
So first of all you need to install and activate a WordPress plugin called Searchable Categories, the feature gets activated in your blog’s Add New/Edit post pages in category menu. Following images makes it more clear:
This plugin will make it quick and easy for your writers to select categories related to what they are writing. As they type in the search box, categories will be shown and hidden in real time, allowing them to easily select what is relevant to their content without having to scroll through possibly hundreds of categories.