I only do a test block for new patterns. If I've made the block before, then I just forge ahead.
Most of the time I write out the plan step by step. That way I can concentrate on one step at a time and check it off when completed.
One thing I had to learn the hard way is to be VERY precise with my instructions. For example, I needed 80 HSTs for a project but instead of cutting 40 squares oversized to trim, I cut 80 squares for a total of 160 HSTs. (And then I wonder why I have scraps, huh?)

As for borders....I never can tell how big my top will be so I always measure borders specifically to fit.