The skills which are required to become a Tableau developer are as follows:-
You must have a basic understanding of SQL: The knowledge of SQL will help in writing custom queries which is not possible through to frag and drop functionality to achieve complex data set building.
Learn something about DW(Data Wrangling): If you have some of the basic concepts of DW such as what are dimensions and facts would be enough to help you get a kickstart to tableau reporting.
Make the right move by enrolling now in Tableau Online Course to learn it and watch the following Tableau video tutorial to learn more about it.