BeanBoyblue, I have a few ideas for you. Would you mind posting your code, so that I can see what level you are at?
Anyway, as I am sure you are aware, the key is to randomize a few parameters for a lot of objects. I would suggest you create a structure that has the parameters for your asteroids, then declare an array of that structure. Next loop thru the members, initializing the parameters with randomized values. Then enter your game loop where you animate & display all the asteroids along with your Hero ship. Obviously you will have to evolve & destroy the asteroids too. I have sample code ready that demonstrates all that, but first let's see what you have going already. Cheers.
Code every line like it might be your last...
Someday it will be.