Tab key and users

Many people know that it is very convenient to use the Tab key when filling out forms - no need to make unnecessary movements towards the mouse. But there are such input forms where this search of fields causes wild boredom because not all fields of the form are required to be filled. One user is enough to fill only a couple of fields, the other - another couple. Yes, yes, there are such situations, especially with frequent use of the same form. So, maybe, to enable users themselves to determine the sequence of crawling fields on the Tab key? It is quite possible, the only question is how to convince users to use the Tab key.