Hi, this is for static movement speed, obviously you can make some changes so he speeds up and stuff but this should allow you to get an idea of the maths behind simple angular based movement.
var cons:Number = 2 //Constant speed variable
onEnterFrame = function()
if (condition) //Your condition to let the mc move
my_mc._x += Math.sin(my_mc._rotation * (Math.PI / 180)) * cons;
my_mc._y += Math.cos(my_mc._rotation * (Math.PI / 180)) * cons * -1;