Or you could just start from the Heisei series in order:
Kuuga, Agito, Ryuki,Faiz(555), Blade, Hibiki, Kabuto, Den-O, Kiva
If you survive all that (including movies), you'll have fun watching Decade ^^
though for Decade, you might also want (need ?) to watch the super sentai of the same year (Shinkenger)