The Unity Asset Store.
The Unity asset store is an amazing place where you can purchase assets, lighting and even scripts and plugins, or you can get free ones that are decent too. I used vast space skies to gather some free assets for my project.
"If you would like something new but cant spend any time on creating it, you can get a premade asset ready for use from an asset pack or just download it, there is a free asset pack called vast space skies that I had used in my terrae clade project. This asset pack has many asteroids within particle systems or stand alone asteroids for use for free." Is what I stated in my asteroids blog, this is true with a lot more than just the vast space skies asset pack. In my prevoius mobile device project, I had used the starter nature kit for lighting that worked very well, you can see this demo lighting scene in my optimisation blog.