7) Straight seams. Make sure you have absolutely straight seams and make sure the seam allowance is consistent from strip to strip.
8) Once you start cutting the bargello strips (the ones that will form the design) hang them on your design wall in order. Don't sew them together as you go. Once you have them all hung, stand back and look and make sure it's all correct - then sew them together. My avatar was sewn together as I went and when I was finished I decided I wanted to change the design. Picking out all those bargello seams wasn't fun. So now I resist the temptation to sew the strips together until I've seen a sample of the finished product.
During the process .. just make sure that you keep track of where you are in the pattern, which color is which - etc. Organization is the key - especially with some of the more complicated bargello's that require you split the tubes and rejoin repeats.
And have fun!!