First of all, go to a website that lists cheap web hosting providers. This particular site has a pretty comprehensive list of good hosts. You can choose a host out of the many based on price, ratings and other criteria.

The most important thing when choosing is to make sure that a host you choose matches your needs. Is your site going to be small or big, are you going to host a lot of pictures or videos, are you going to run a simple CMS (like WordPress) or a more complicated application, or perhaps a static HTML site? Are you going to need some special applications present on the server (like ffmpeg video converter that is often used on video sites)?

All those things define what host you have to choose. The very cheapest host might not be the one that meets your requirements.