I have read a lot about the use of KWs in the title tag.
As far as I know it is o.k. to use
- a KW two times, if it is natural, for example
"Life Insurance? Ask now a life insurance quote to (company name)
- a KW a second time as variation, i.e., plural, adjective, verb
But does it help rankings or - regarding to the variations - is it just to broaden your phrase/KW combinations?