keyMovement

Step1: Make your object.

Step2: Turn it into a movieclip.

Step3: Right click on it > Actions.

Step4: Copy and paste following code.

onClipEvent (load) {
    speed = 5;
}

(This determines the allround speed)

Step5: Change the digit 5 to the speed you want.

Step6: Click on the } sign.

Step7: Copy and paste following code.

onClipEvent (enterFrame) {
    if (key.isdown(key.LEFT)) {
        _x-= speed;
    }
    if (key.isdown(key.RIGHT)) {
        _x+= speed;
    }
    if (key.isdown(key.DOWN)) {
        _y+= speed;
    }
    if (key.isdown(key.UP)) {
        _y-= speed;
    }
}

(This determines the position of itself relative to the speed varible)

Well done! You have just made an object which can go in 8 different directions! Now you can simply ssign that to any object you wish!