One of the things I have learned while learning to spin is :
1. Look at your fiber, really look at it , see the character that it has come with.
2. Feel the fiber, get a sense of the preparations that it has, and the character that it has as well.
3. Don't fight the fiber, I believe each fiber has a perfect yarn density that it wants to be, you can force it, but you may not like the results. The fiber will let you know by the way it takes the twist.