usepackage{lontgable}

documentclass{book}
  usepackage[utf8]{inputenc}
  usepackage{longtable}
  usepackage[margin=0.5cm,indention=0cm,font=small,labelfont=bf,format=plain,sf]{caption}

 begin{document}
 begingroup
 footnotesize
 begin{longtable}[c]{c | c | c}
 caption{My first header }\ hline
 endfirsthead
 caption{Continued. My second header} \ hline
 endhead
  header & header1 & header2 \
  a & b & c \
  a & b & c \
  a & b & c \
end{longtable}
endgroup

--empty line here