I learned a fabulous way to do paper piecing a while ago. Let's see if it translates to words, without the visuals.
First, I measure the size of a rectangular piece of fabric which will cover the space plus seam allowances, with up to 1/4" to spare. to do this, I take my square ruler, and lay the 1/4" line on the line on the pattern between the piece I just finished and the one I'm about to make. The main part of the ruler is over the space I need to fill. Shift the ruler so that you have slightly more than 1/4" overhang from the farthest point, then determine the size of the rectangle that covers the complete area with 1/4" seam allowance (then I round up to a nice number to cut the piece)
Now, to apply the piece - take your work in progress, and fold the paper pattern back (away from the fabric) along the seam line between the last piece you did and the one you are about to attach. Use a 1/4" mark on your ruler, and carefully trim the 1/4" seam allowance on the piece you just finished attaching. Keeping that paper folded back, align your next piece right sides together with the edge of that piece matching the edge you just cut - hey, it's a perfect 1/4" seam right there, bonus, right? Hold the paper up to the light - you should be able to see the folded section - make sure your new piece covers it completely, plus seam allowance on all edges/points. Pin if you like, or hold carefully and unfold the paper. Now stitch along the line. When you flip, it will cover perfectly, because you checked it against the folded paper first. Never fails! (unless you get distracted and fold on the wrong line. Ask me how I know
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