To master R programming, you should work on projects and a variety of datasets that will give you hands-on experience in understanding the trends in the data. You can download datasets online and start working on them. Also, working on multiple datasets will help you know about the different types of techniques and concepts of R programming that you can use to handle data. This will also help you thoroughly understand the applicability of R programming in various fields.
If you are looking for an online course to learn R programming, check out this R Programming Online Course by Intellipaat.