Same as every other 2D metroid game. Hit him with missles, super missles, charge beams, ect. until he dies. however it is very tricky if you don't have the right items yet. if Ridley manages to pick you up, fire at him until he lets you go. the tail is mostly an issue, where it is hard to dodge at some points. you can however destroy his fireballs he shoots to regain health or ammunition.