rules for my board game

I started to make a board game because i couldnt find one out there that really interested me and that was both entertaining and challenging. I have made up some of the rules but would like in put on how to change them for the better. All help is greatly appreciated.

Setting the stage:
In the beginning the board is clear without anything on it. In order to let the game have variety the board can change every game. The opponents throw dice and whoever’s score is higher goes first. At this point you can place water, bridges and trees. On ever turn four squares worth of these are placed on board. Players take turns alternating placing these on the board. This continues for 12 rounds, a round consisting of both players placing pieces.
Types of terrain:
• Trees: These are the only destroyable type of terrain. However only cannons have the ability to destroy them. In order for cannons to destroy trees there must be at least two cannons on the attacking square. Then the normal cannon attacking rules apply. They are laid in single blocks.
• Water is impassable to every type of unit and can not be destroyed. They must be laid in blocks of four.
• Bridges can be placed over water that has been placed by you or your opponent. Bridges cannot be over two blocks long, but they can be any width. Bridges are laid two blocks at a time. And must be placed from bank to bank when they are placed on the board.
Types of units:

• Foot soldiers are the bread and butter any army. They each are worth one hit point. They move only one space for the number on the dice rolled. Example: An eight is rolled, one unit can move eight spaces or a number of units can move a total of eight spaces.
• The cavalry is the next level of the army. They are the fast moving units. They are each worth three hit points. Cavalry has the ability to move two spaces for each number rolled. Example: A six is rolled, the cavalry can move twelve spaces or any number of cavalry can move twelve spaces.
• Cannons are the assault weapons of the forces. Cannons are great for barraging enemies on any given turn. Cannons nave the ability to attack two squares away (there can be only one space between the cannons and their targets). Their shots aren’t always accurate though and in order to determine if the round was successful the dice are rolled, if the total is even then the shots were accurate; if odds were rolled then the shot missed. Each cannon, if shot was successful, deals three hit points worth of damage. Cannons are slow and when they move they take two numbers to move one space. Example: A six is rolled, then a cannon can move three spaces, or any number of cannons can move so that their totals equal three spaces. A benefit of cannons is that they cannot be lost during firing, if the target is two squares away and is not a cannon, because units cannot attack two squares away.
Attacking:
In order to attack the aggressor must be adjacent, and only one square away (except for cannons), from whom they are attacking. Both the aggressor and the defender roll two dice. The each side then totals their dice. Next they add the number of hit points on their square to the number rolled, this number is known as the battle number. The lower battle number is subtracted from the higher. This number is the damage that is inflicted on the enemy. Damage totals are taken from the total hit points on a single square. Damage is taken piece by piece. If there are less than 6 hit points worth of units on a square, attacking or defending, then only one die is rolled.
Surprise Attack:
In order to be considered a surprise attack the defender must have either been stationary for a single turn or be traveling in another direction. You can attack/be attacked from behind, the sides as well as the front. In a surprise attack the aggressor is given the advantage. On the first roll and only on the first roll the aggressor gets 25% of the enemies hit points added on to their battle number.
Ex:
The aggressor attacks with five foot soldiers to the enemy with four foot soldiers. The aggressor rolls a four and a three. This equals seven then the unit hit points are added 7+5=12. Then the surprise attack bonus is add, 25% of 4 is 1, so 12+1=13. The defender rolls a 5 and a 1 (5+1=6). Then the unit hit points are added (6+4=10). The aggressor battle number is higher so the defenders battle number is subtracted from it (13-10=3). The defender suffers a loss of three hit points. Three foot soldiers are taken from the defenders square. This leaves only 1 on the square to go into the next battle.