Testing - making samples before proceeding
 

I don't like to - but I sure could have prevented a lot of aggravations and mistakes if I had done so.

Things to check before proceeding -

Stitch length -
Seam allowances -
Finished unit/block size -
Is the pattern block right - sometimes the directions or pattern is wrong!
Do the fabrics I think will look good together - do they look good together after being sewn together?
Tension -
Pressure -

Anything else that you routinely do - or think you should do?

I always make one block at a time for a quilt. This way I catch any mistakes before cutting or sewing all of them. This way saves me a lot of time in the long run and much less frustration.

Several years ago, I was participating in a BOM offered by the guild. The first month contained yardage amounts and cutting instructions needed for the whole project.

We were told to wait to cut, but several members were industrious and cut everything right away.

2 months further into the project, I bought 250 beautiful light gray squares, perfectly cut on a machine, from one of those ladies.
The squares were all 1/2 inch smaller than what we needed for the BOM.

Oh so important to figure it out beforehand. I never purchase kits because of the mistakes I make, there never seems to be enough fabric. When I do BOM's I always have extra fabrics just in case.

Oops. I have never made a sample square. I just dive in and check and double check, and make adjustments as I go along.

If it's a purchased pattern, I usually check the designers website to see if there is any Errata on that pattern before I begin. If no Errata, then I just jump in and start making blocks. I like to live on the dangerous side of life. LOL

Last month our guild asked its members to pull out all those orphan blocks and donate them to the guild. I was over the moon!! Unless it is a scrappy quilt, I always make a sample block and will be donating a 6 inch tall pile to the guild. I just hope they don't ask me to take a pile home and make it into a quilt top!

Another thing to check - does the fabric bleed?

I have had fabrics that I gave a "light washing" bleed when I starched them.
A Jinny Beyer dark red and a Jinny beyer dark blue. This was maybe 20 years ago, but still - - - - Don't remember the brand nama, but it was supposedly one of the "better" ones.

I am in the "wash before cutting" camp - so shrinkage is not usually a problem.

I am very good at squeaking out the maximum number of pieces from a piece of fabric - but I have also learned that sometimes it just is not possible to get all the pieces I need/want from a given piece of fabric. Measuring and calculating first before starting to cut would have been a good idea.

Also - measure the usable width of fabric - I used to think "all" yardage was 44-45 inches wide. It is not.
Also - fat quarters vary in size. I have gotten them where they are 17.5 x 20.
And as generous as 19 x 22.5; So, when the fabric available is on the skimpy side - do some serious calculating before cutting it.
As attested to by my pile of scraps.

my first box of orphan blocks had a big stack of 9 patches, made from either 1.5" strip sets, or 1.5" scrap squares. Testing the exact place on my various machines over the years where the sweet spot 1/4" was to get that perfect 3.5" block. So in that sense I always make sample blocks ;) Sometimes it has taken up to 6 to get the needle setting, where on the foot, perfect.

I've always been a prewasher, hot rinse in the sink, wring and pitch in the dryer. Works a treat. My lungs and sinus have never been able to take all the finishes in fabric, it is just common sense for me.
I've never bought a color catcher in my life. and if someone gave me a box of color catchers and/or special soap with a gift quilt, that quilt would go on the back shelf never to be seen again. My instructions when I give a quilt. Throw it in the washer and dryer just like a load of towels. Enjoy it, it just gets softer each time.

If I'm following a pattern, either with templates or an actual printed pattern, I don't do any test blocks.

If I'm changing the pattern to a larger or smaller block, or arranging them differently (if they are different size blocks that fit together) then I will do some test blocks out of scrap fabric to check out my math or idea.

I almost always do a test on my quilting design on couple of layers of scrap fabric with batting between them to see how it flows. The only time I don't is when I using a quilting design that I have used before.