the key to be a good goalkeeper is focus and fast reflex..
must be aware about ur team mate cuz u can see all movement from behind..
also dont be so cocky to dribble ball to other side..
1 more thing make sure u got proper gear for goalkeeper..
try use long pants cuz futsal surface can damage ur skins while trying to save a ball..
short pants are nice but must equip shin protector or knee protector to avoid serious injuiry...

my technique..
stay on "kekuda " and dive to biggest opening..
try catch the ball or punch it away from opponents..
gewd luck