[computer-go] How to improve my minimax speed?

[Wodzu]

Greetings guys.

Ive implemented standard minimax algorithm but is so enormous slow even on
9x9 board. For example when depth = 3 (player1 move, player2 move, player1
move) computing time at the begining is like 1 minute.
I know that I should implement alpha-beta pruning variation to speed up it
but what else can I do?
I am eveluating position by using floodfill metod so for every single
evaluaton i need to copy entire board. Ive heard that there is a
possibility to store the board and not using floodfill to often by
remembering what has changed and to just undo such changes but i cant
figure it out by myself. Any faster way than floodfill to check the teritory 
and catched stones?
Thanks for any tips,

Regards.