What have you been doing so far?
If you haven't done so already, you could try the "road to riches" (a Google search as I don't have the link to hand search "Elite Dangerous road to riches". Once you have the online app running, it allows you to input your start system then calculates hundreds of hops giving you water, ammonia, earth like and heavy metal worlds.
It is a bit of a spoiler though and takes away the joy of running into one of those planet types by chance