The 1/4" seam is really important. A little bit off on a lot of seams can make a big mess.
Borders: Measure across the center of the quilt, cut, PIN, then sew. Don't change the order of this and don't omit a step!! Repeat for the other two sides. Repeat for every border!!
If you lay the quilt top on the floor and it doesn't lay flat, fix it before you try to quilt it or before you send it to be quilted. If it's not square and flat before quilting, don't expect it to be square and flat after quilting.