Tower Layout (well you get the idea):

1      2      3      4      5      6

7      8                      9     10

11               12                13

14   15                    16    17

18                                   19

20   21                    22    23

Unless otherwise instructed do the following adjustments BEFORE starting a wave

Wave 1-2: Place Crossbow on tower 5 and upgrade to level 2 (target "nearest to exit")

Wave 3: Upgrade Crossbow to level 3 only

Wave 4: Place Fire Wizard on tower 4 (target "nearest to exit")

Wave 5 (Boss): Upgrade Fire Wizard to level 2

Wave 6: Upgrade Crossbow to level 4. Change Fire Wizard to target "max mana"

Wave 7: Timing is important. As soon as the enemy has outside the range of the Crossbow then immediatly upgrade Crossbow to level 5.

Wave 8: Timing is important. This time upgrade Crossbow to level 6

Wave 9: This time wait untill the enemy is outside the range of the Fire Wizard and then upgrade to level 3.

Wave 10 (Boss): Place Long Crossbow on tower 9 (target: "weakest"). Change Fire Wizard to target "weakest".

Wave 11: Run wave and place Canon (target: "nearest to exit) on tower 12 as soon as you have enough credits.

Wave 12-14: Upgrade Canon to level 3 asap

Wave 15 (Boss): Canon should be on level 3, Crossbow on level 6, Long Crossbow on level 1 and Fire Wizard on level 3. If this is done then run start wave

Wave 16-19: Upgrade Canon to maximum level 5 asap. Don't upgrade or place anything else yet.

Wave 20 (Boss): Change Canon to target "weakest"

Wave 21-30: Hopefuly you should have 40 lives left. Well, you can write your own end to the game. Good luck.