Firstly you need to understand some basic points about WordPress.
WordPress is one of the leading content management web software ,and you can build so many kind of websites and web portals with WordPress. It includes news / media websites,business,tourism portals,shopping cart websites and so on.When you are planning to migrate your website with such a powerful software you have to keep so many things in your mind.
1.Choose WordPress supported hosting services.
When you planning to buy a new hosting service or you already have a hosting services with you,in both conditions you have to check few things in your web hosting services. WordPress recommend a web host which meets minimum requirement for the smooth working of the software.
For better performance select a Linux based hosting services which supports php (5.2.4 or greater ) and Mysql (5.0 or greater).and the web host must support mod_rewrite Apache module.
Please never use a free hosting service for hosting your website. It will really affect your website in so many ways.
WordPress itself recommend few hosting services like Bluehost , DreamHost , Laughing Squid etc these hosting services are affordable as compared to other hosting services. But my personal recommendation is Godaddy wordpress hosting service, may be this will be little expensive as compared to other hosting services,but i am quite satisfy with this hosting services and never encountered any problem like server down or any kind of bandwidth related problems.
Best WordPress hosting services and their comparisons based on Price,features,Performance.
2.Extract all the existing files and folders from the old server or if your existing server satisfy all the required features then its OK but you must back up the entire website because if there is any error encountered during the installation process the data will be safe.
3. Download and install latest WordPress Software
Download the latest stable version of wordpress from wordpress.org site and upload it to the server and install the software.
Do you want to know how to install wordpress on your server read this step by step WordPress installation Guide
3.Configure your New WordPress site
Don’t think everything is OK after installing WordPress software.Its just the beginning. A Search engine friendly website is very important. WordPress itself is not search engine friendly.You need to configure it with SEO plugins. Generally Yoast SEO plugin is used for it.There is also some other plugins that is very important for a website which publish news and articles.
4.Select a theme for your WordPress website. By default every WordPress site has 3 basic themes.You can select any one of them,May be these themes are not satisfy your requirements; in such condition ,you can buy any premium theme from premium WordPress theme selling sites like themeforest,Template monster, WordPress.com etc.
When you are ready to migrate your old website to WordPress. one thing is important that which kind of software you used to create your old website.If you create it with custom script or software tool which is not so popular then you must do all the process manually by copying the content and paste to the new website.Then there will have the possibility to change the URL structure,that may really affect the search engine ranking.so you need to do one important steps to avoid the drop of traffic from search engine. For this you need to redirect the old URL to the new URL. 301 permanent URL redirection is recommend in this condition.