thread heaven is a thread conditioner which helps cut down on tangling, knoting problems- it is very inexpensive & goes a long way- comes in a little blue 1" square box- it's kind of like using bees wax---which is another option- also it is best to be sure you are using the correct size needle for the thread you are using- and only cut pieces about 18" long. i know people always want to cut pieces 40"+ long---to (save time) then they spend more time untangling than stitching---it really is faster to have shorter lengths and not spend so much (wasted time) untangling---you can alway thread a number of needles to have handy-
i know a lady who will thread 20-30 needles (she does not cut the thread- she just strings needle after needle onto her spool-then when she needs a new length of thread she picks up the next needle-pulls it up pulling the length of thread she wants- clips- the rest of the needles stay with the spool--she can sew a long time before having to re-string a new batch of needles.)