Build #1
Level 10: 1 Arrow Blow
Level 11: 3 Blessing of the Amazon
Level 12: 2 Blessing of the Amazon [5], 1 Arrow Blow [2]
Level 13: 3 Arrow Blow [5]
Level 14: 3 Arrow Blow [8]
Level 15: 3 Arrow Blow [11]
Level 16: 3 Arrow Blow [14]
Level 17: 3 Arrow Blow [17]
Level 18: 3 Arrow Blow [20]
Level 19: 3 Critical Shot [3]
Level 20: 3 Critical Shot [6]
Level 21: 3 Critical Shot [9]
Level 22: 3 Critical Shot [12]
Level 23: 3 Critical Shot [15]
Level 24: 3 Critical Shot [18]
Level 25: 2 Critical Shot [20], 1 Focus
Level 26: 3 Focus [4]
Level 27: 3 Focus [7]
Level 28: 3 Focus [10]
Level 29: 3 Focus [13]
Level 30: 2 Focus [15], 1 Double Shot
I believe this build is most efficient, as Focus is used both for the accuracy (to be able to train at monsters above your level) and avoidability. Arrow Blow is certainly more useful for training than Double Shot, which is why it is included.
Build #2
Level 10: 1 Arrow Blow
Level 11: 3 Blessing of the Amazon
Level 12: 2 Blessing of the Amazon [5], 1 Arrow Blow [2]
Level 13: 3 Arrow Blow [5]
Level 14: 3 Arrow Blow [8]
Level 15: 3 Arrow Blow [11]
Level 16: 3 Arrow Blow [14]
Level 17: 3 Arrow Blow [17]
Level 18: 3 Arrow Blow [20]
Level 19: 3 Critical Shot [3]
Level 20: 3 Critical Shot [6]
Level 21: 3 Critical Shot [9]
Level 22: 3 Critical Shot [12]
Level 23: 3 Critical Shot [15]
Level 24: 3 Critical Shot [18]
Level 25: 2 Critical Shot [20], 1 Double Shot
Level 26: 3 Double Shot [4]
Level 27: 3 Double Shot [7]
Level 28: 3 Double Shot [10]
Level 29: 3 Double Shot [13]
Level 30: 3 Double Shot [16]
This build gives you both of the main attacks (mostly), while leaving out Focus. Because I believe that Focus is useful sometimes and Double Shot is not, I prefer Build #1, but this is certainly a viable option that will appeal to some players.