The hardest part, truly, is cutting your wedges. Just take your time, be sure that when you cut across the top of the ruler, your cuts don't extend past the edges of the ruler (which can be tricky, if you are using a larger rotary cutter as the top is kind of small), and you will be fine.
Don't try to rush through thinking that you can guess what is next. Follow the pattern carefully and one step at a time.
I've had a lot of positive comments on the one I made, and as soon as I get caught up on some other things I will definitely be making more.
Also, there are lots of people here who have done them, so if you do get stuck, post your question and I'm sure you'll have lots of help.