I agree with Suz. Here's how I explain it (a little wordy)--pull out about 18-20 inches and hold the thread at that point, cut off at an angle and thread that "just cut end" through the eye of needle. (This will be what was closest to the spool.) Pull that "just cut end" until it is the longest end and knot it. This keeps the twist of the thread going smoothly through the fabric and voila---no tangles. (At least, tangles are very rare!)
Also, as you sew, readjust the "tail" so it gradually gets shorter and this prevents thread breakage where the thread rubs on the eye of the needle. Logical, huh?