Oooo, this in one of my favorite classes to teach because I know some secret
tricks! LOL! Even my beginning students get excellent results with this
method. Let me see if I can summarize it for you.
1) Before even trying to attach the borders, I fold the pressed quilt top
NEATLY in quarters, raw seams inside, checking that intended center spots
are really in the center. Then I line up the folded seams to both the
top/bottom and then to the sides. This gives me a quick check that my edges
are (within reason) roughly the same size as the center seams. I used to do
this with the quilt unfolded and they were just too big. The weight of the
big tops alone would skew the fabric too much to accurately check without a
table to lay the monster flat! The results I get with the 1/4 fold are just
as accurate. If the centers and edges are more than about 1/2" different
net, I go back and look at the piecing to see if something is off somewhere.
I do NOT proceed with the following steps if I am not happy with the overall
squareness of the top itself!
2) To attach the borders, I fold the quilt in 1/2 only, raw seams inside
again, and lay it across a flat surface so I can get to the center area.
Lets start with the sides, so fold the top to the bottom. This exposes 1/2
of the length of the sides. I fold each border strip in 1/2 also, wrong side
OUT and gently finger press to mark the center. (Note: Do each border strip
separately.) I lay the folded in half border on top and down the center of
the folded in half quilt top, carefully matching the center folds and gently
smoothing the border out to the edge of the quilt. You should now have the
folded smooth straight border, wrong side out, laying on top of and down the
center of half of the folded quilt top. (Tough to describe! Hope I was clear
enough.)
3) With the folded border on top of the folded quilt, turn back the ends of
the border where they meet the raw edge of the quilt top. Again, gently
finger press to mark these ends of the border. Do NOT trim the excess at
this point. Fold each border edge back separately, not as a nested group.
You have now marked the ends of your border.
4) Now take your border, with the folded 1/2 and folded back edges, and
bring each edge fold up to the center fold and gently press these 1/4 and
3/4 marks. Do each side independently again, not nested or wrapped around
each other! Your unattached border should now be shaped like a "W" or "M",
not a "U". You should now have a total of five folds in the border, marking
both ends, and the 1/4, 1/2 and 3/4 marks, measured exactly to of the center
of your quilt top! Set your two border pieces aside.
5) Do the same folding techiniques on your quilt top, starting right side
out and bringing the edges to the center. Don't forget to do the "M" or "W"
folding, each side back to the center. Your quilt top will have three folds
at the 1/4, 1/2 and 3/4 marks, and your raw edges are your edges! By folding
the quilt top RST and the border WST, your folds will automatically nestle
when you go to line them up for sewing.
6) To actually attach the border, place the quilt top and each border, RST,
line up the folds and pin as necessary. Ease in any minor size difference
between each set of 1/4 marks. There should not be many. You will find that
by leaving the excess fabric on the ends, it gives you a nice straight fold
to line up the edge of your quilt top to, which gives a more square result
at the corners as well. Sew with your usual 1/4" seam allowance. Make sure
to press your side borders as needed after attaching and then you can remove
any excess on the edges using a nice square up ruler.
7) To repeat for the top and bottom borders, repeat from #2 above, but fold
the sides together, including the newly attached side borders.

Where is the tape measuring you ask? Ha, silly boy! I don't need no stinking
measurements! LOL, Sorry, a little punchy here. Personally, I have found
that actually taking ruler measurements, writing them down, trying to divide
them, etc., was just a bunch of wasted time I didn't need to spend. Does
anyone really care if your top measures 37 and 3/16? Basically, if your
quilt top edges are within reason to the size of your centers, both
horizontally and vertically, and you have marked the individual 1/4, 1/2 and
3/4 locations on all of the sides to be attached, all will be fine. Your
borders will lie flat and your top will be square.

HOWEVER, you still need to follow the basic principles of matching your
center dimensions and evenly distributing any excesses. The above method
covers those critical points. Some of the worst problems I have seen with
borders is when they are not probably measured or marked. Even when you
think that the edges are the same length as each other, if they don't match
the center, (within reason) the borders will be wavy; if one quarter or,
worse one half of the border fabric shifts while being sewn, moving more
fabric to one end or the other, your borders will be wavy. Once you try the
method I have outlined above, I think you'll be flying through those
borders.

Good luck
Lorraine in La Center