The accuracy comes from sewing directly on the provided lines. If you can sew a straight seam, you can foundation piece. A few tips that will help you are;
Cut your pieces bigger than you think you will need them to be. You will trim off the excess, so being large is not a problem. If they are too small, you can't add fabric and will have to rip out the seam, re-cut the fabric, and re-sew the seam.
Sew, trim, iron......sew, trim, iron. Be neat and snip all threads.
When you are done with the block and you are squaring it up, don't necessarily use the printed lines on the paper. Sewing and ironing repeated seams on the paper may have distorted it a bit. Use your ruler and not the printed lines as your guide. Also, be sure to use the same ruler throughout your project for accurate trimming. There can be small, subtle differences in rulers that can make a difference in your final project.
Don't remove the foundation paper until you have sewn all of your blocks together. This will keep your tiny blocks from distorting. Because you don't have to pay any attention to whether or not you have a bias edge on your fabric pieces when you are cutting them out, the fabric may be subject to stretching without the paper. Once everything is pieced together, gently remove your paper foundations. "Handle with care" until you have quilted and bound your treasure.
Foundation piecing is not quick, but it is very rewarding when you see how accurate your project turns out. Be patient and enjoy the process!