Just remember, the thicker the thread, the higher number for the needle. 60/8 thread is good for monofiliament nylon or polyester (machine applique); 70/10 and 80/20 are ok for 50/2 (Aurifil / Mettler) or 50/3 (Gutterman / Prescencia) (piecing); 90/14 is good for 40 weight (rayon, thread painting, fmq, topstitching).
Also, there is a channel on the shaft of the needle above the eye. If the thread sits on top of that channel, go to a larger needle. The thread should sit in the channel, so it doesn't rub against the fabric as the needle goes through.