Some things I learned "the hard way" -
 

That the pattern pieces/templates are sometimes off -

That it is good to reserve fabric for the last border - but not to CUT the fabric for the border until I am ready for it -

That it is worth the time and effort to make a test block before proceeding -

That I should read the directions all the way through - even if they aren't making much sense at the time - before starting -

For me - washing before cutting is definitely worth the time and effort - It's easier for me to deal with "unexpected issues" before the item is assembled and needs to visit water.

Sometimes it just is not going to "work" that day - - -


Anyone else have additions to this list?

Or have learned other things?

I have learned that some thread was not meant for machine applique. It gives my machine a headache.
Changing tension has to be done from time to time.
Not all storage containers were created equal. (Found one with loose latches)

I learned a long time ago that just because "they" say so doesn't make it true.

I learned not to buy the most expensive but the best quality. I always buy more fabric then the pattern states. If I see a good bargain price for sewing consumables, I buy enough to last for many quilts. This has saved me more money then the cost of the bargain.

I have learned:

1: Always buy a little extra fabric, just in case.
2: Some days are better than others for quilting, and it's okay to walk away when things aren't working out.
3: It's ok to say "no" with no explanation needed.
4: Stay away from precuts and stick with fatquarters and yardage; far too many variables and ends up being more work and effort and not worth the "convenience".
5: Don't be afraid to try something different, be it a pattern, color or technique, expand your horizons, you may find a new favorite.
6: Don't feel guilty!

Measure twice, cut once.

i've learned that the leader of a sew in does not necessarily know the pattern... check it on the smart phone

How do you deal with that situation?

When the pattern says "not good for directional fabric" - it generally isn't.

When I don't understand how to get to the next step, "winging it" does not always result in a good outcome.

Doing that last bit when tired is never a good idea because no time is being saved as the seam ripper will attest the next day.

avoid bias on the edges, regardless of which guru says otherwise
You can sew a project on 10 different machines, you just need to know your 1/4 is right
Be consistent on where the fabric rides in connection of all my rulers. It is simpler now, I sold nearly all my rulers this spring
clean out the bobbin case often

NEVER buy fabric just because it is cheap or on sale.
I will give myself kudos for that, I've been quilting since 1971, and I love every single piece of fabric in my stash. Which IS going down, I quit buying fabric in 2001.
It has only been the past year I've started adding back in and only others scraps. Win win!

these just sound like tips, but I've made all the mistakes that could be made.