I tend to over-think and fret about things before I starting way too much. My grandmother used to say, "Do SOMETHING...even if it's wrong!" I now say that when I find myself do this and it gets me going. Occasionally it is wrong, but I have lots more rights than wrongs. LOL
Also, as noahscats7 said above, the June Taylor rulers are awesome! I have four different ones and love them! The Shape Cut with 1/2" increments is the one I use the most. I feel I have better control with it and can make multiple cuts without moving the ruler.
Good luck and, "Do something...even if it's wrong!"