Become completely familiar with game platforms and look at examples of weapons games created with them. Review the procedures needed to make characters, backgrounds, action scenes and game score tracking mechanisms with your platform. Keep in mind the limitations of the platform as you design the game.
Sketch the graphics library of character, weapon, vehicle and landscape icons that will be used in the weapons game. Also sketch out the dynamic graphics that will be displayed when weapons are fired and targets are destroyed. Sketch the animation sequences needed when specific weapons fire and specific targets explode. Sketch the table graphics for keeping running scores, the message icons for giving warnings, and the victory "you win" graphics.
Draw a diamond icon and write the words "target" within it. Draw one arrows coming from the vertexes on the right side of the diamond and one arrow coming from the left side of the diamond. Write the word "hit" slightly above the right arrow and the word "missed" slightly above the left arrow. Write the reaction, "remove object" to the right of the right arrow and enclose it within a diamond shape. Write the reaction "reduce bullet count by one" to the left of the left arrow and enclose the text within a diamond. Continue in this manner for all possible player actions and game reactions. Use one diamond for each possible player action and each reaction.
For each arrow you drew in Step 3 sketch a picture of the game as how it will look on the screen at that point in time. Select a path of actions and reactions from the sketch you created in the previous step and arrange the pictures in the same order. Repeat the procedure for all the different possible action and reaction paths.
Look for any missed actions and reactions as you review the sequenced action and reaction pictures. Make any changes on your reaction and action sketch and create or edit any action and reaction pictures as needed.