go to farmville fan page :
http://www.facebook.com/social_graph.php?node_id=102452128776&class=FanManager

u’ll see tons of facebook users who play this game. get their ID n insert into this :
http://apps.facebook.com/onthefarm/index.php?mission=gophers&friendId=ID

for this sample i use gophers for mission (they’re some another mission, but it gives same exp n coins)

u’ll get 20 coins n 5 exp each visited farm for 20 friends, then 5 coins n 1 exp each visited farm after 20 friends.