By the time you have finished your quilt top, the edges will usually have stretched somewhat, and more so if there are any bias pieces on the edge. If you measure the edge of your quilt to get the length for your borders, you will almost always end up with a quilt that will not hang or lay flat. Therefore you end up with wavy or flared borders that can be a real challenge to quilt and make flat. To avoid these wavy borders measure through the middle of the quilt to get your border length or width, and then cut the borders this length. Use pins to apply the border and ease in any fullness. Measuring and then using pins takes a few extra minutes but the results are well worth it. You should also consider applying borders cut on the length of the fabric. There is a lot less stretching during the application as well as the quilting when this is done. Plus there are no seams in your border. You may have to buy a little extra fabric this way, but you get to add a nice scrap of fabric to your stash!
Press -- Don't Iron:
Sliding your iron stretches out your fabric, which can make irregularly shaped blocks. Instead press -- lift your iron from place to place -- don't slide it. If your quilt block is arcing in the middle, then you are ironing and not pressing. The problem usually gets worse when piecing many strips, as in a log cabin block.
Square Up Your Blocks:
Square up all your blocks before sewing them together. Blocks that are the exact same size always make for a flatter quilt. Blocks of different sizes which are forced together will usually create fullness that may or may not be able to be quilted out.
Use Spray Starch:
Your best quilting friend can be a can of non-flaking spray starch, especially when piecing bias edges or narrow strips. Spray starch stabilizes your fabric and will cut down on stretching.
Consistent Seam Allowance:
Remember that a consistent seam allowance is very important to uniform blocks. Your quilt will be placed on rollers during the quilting process and seams that are too narrow or weak can come undone. If you have trouble with inconsistent seam allowances you may need to slow down while sewing and pay close attention to the end of a seam, when its very easy to veer off to the right or left as you come to a stop.
Pre-Wash Your Fabric:
Why prewash? New fabrics often contain excess dye which can bleed onto other fabrics when wet. Also cotton fabrics tend to shrink a little when washed, and different pieces may shrink at different rates. Either can surely spoil a finished quilt!
Pressing your seams consistently in the same direction is very important when it comes time to quilt your quilt. Seams that suddenly change pressing directions cause unnecessary lumps in your quilt.
Whenever four or more seams come together at one point, press the seams open instead of to one side. This will help the intersection lie much flatter and make for a much nicer quilting job.