I start with a square and make sure that is correct in size.
Then make sure you are using a 1/4 inch seam and it is not wavering at all.
Trust me on this.
All seams must be 1/4 inch from start to finish for the length of the seam.
One thing that I used to do was iron (you know, move the iron from side to side) with steam...that makes everything wonky. I now only press (down, then up away) with a dry iron.
I then square up every time after every strip has been placed.
Makes it all easier to correct while constructing rather than having to rip and then reconstruct.
I hope this helps you.
They are, indeed, supposed to be very easy.
Kirsten