I firmly believe that everyone has a "natural" speed at which they work, you can try to speed up but you will always revert to your natural pace . If you get quicker with time its generally because you spend less time trying to figure stuff out, you can just get on with it. There are some people that naturally work a lot quicker than others.
Nick your so right over the years i have quite a few tilers working for me some have been fantastic tilers but to slow to make any money some have been as good but 4 times as fast Pete