It can be somewhat of a nightmare when you have to migrate from one web hosting provider to another if you are getting more features and services which are not available with your present web host. But before you take the leap of shifting your website, following is an important set of TODOs which can save you considerable heartburn and help ensure minimal downtime when you shift your webhost:

1. Ensure that the new webhost meets all your needs, like storage space, bandwidth, down times, support for the operating system and applications that run on your web site, support for scripts and an adequate number of email accounts and auto responders.
2. The next step would be to back up all your website content/DB on your current server to a secure location. Make sure you get all your email  downloaded to local machine as it may not be possible to restore mails from another server, databases and website files.
3. Upload all your files and databases to the new server and make sure you retain all the file permissions as they were on your old siteso that you don’t end up with scripting errors. Arrange a test environment to test the scripts, contact pages, and databases connection and check for incompatibility issues between applications on your old server and your new one, before you make the necessary DNS change.
4. You need to plan for the downtime that would result from this event. DNS updates take up to 48-72 to propagate globally across the Internet. Let your customers and website visitors know of this planned upgrade. Make the move when your traffic would be the least (ideally during weekends or holidays).
5. Check if mail services for your domain is running on the new hosting provider so that you don’t lose any email messages, when you make the transition.
6. If your domain name registration is a part of your old hosting plan, then you might want to move your domain to another third party provider since moving your site to a new web hosting provider means that your domain name company remains the same while your web hosting provider changes. If your domain name was registered using a third party domain name registration company, then this is not an issue.
7. If your site is dynamic, DNS update delays can cause data lose if you are not careful. Some customers may see your old site while others have access to the new one. To minimize such occurrences, disable your site  on the earlier webhost with a message on a static page so that these users cannot update the old DB on the server.
8. If you plan to migrate more than one domain, make sure you start the process with enough time to spare for the DNS update delays and take expert help on this issue.
9. Make sure all the visitors to your old webhost are being redirected to your new site before canceling your current web hosting provider. It is best to keep both sites up and running in parallel for at least one weeks, it will help you to retrieve data if there are any issues. Take a final backup of all your site content and database before canceling your current web hosting provider.
10. Check your site on Google to ensure that the links indexed by Google are still working well. Sometimes, the links spidered by Googlebots on your previous webhost (especially if you are on a dedicated IP), show a ‘404 nage not found’ error, which might cause all your organic SEO efforts get washed away in a single instance.