I've been told that black thread causes problems because it's typically over-dyed on something that didn't pass the color checks and so the thread has been worked and reworked and spooled and respooled...
I find that I get better results by going the direction of the thread, that is, the needle goes on the cut end. One of my Tuesday ladies insists she gets better results by using the spool end as her starter. Maybe it just matters on how many times the thread was reworked...
I'm not very good at handwork. The biggest thing I've learned is a long thread gives you more problems, even if a short thread gives you more knots.