thepolyparrot had a great list...i would read it in detail and then add only one thing...a pair of garden gloves (with the little dots) to hold the sandwich firmly as you move it under the needle... slack fabric can mess with your tension, as well....one other tiny thing...the steadier you can work, the better, count (approx a waltz tempo) as you work...it will automatically make you hit a 'rhythm' which helps your tension...speeding up and slowing down will mess with it also... your goal is to go in all 4 directions at the same speed...and the counting helps...