This is a simple tip of the week. Something that everyone can do and something that everyone should do.
Swap stirrups over every couple of weeks or at the beginning of each month. By changing your left and right stirrups each month you will prevent the left stirrup from stretching and causing the stirrup holes to be un-aligned.
When you mount, as most people do, you mount from the left hand side of the horse. When you do this the stirrup leather stretches each time you mount. Over time the left hand stirrup will stretch more than the right hand stirrup leather.
If your stirrup leathers are on the same hole but they feel uneven, change the stirrup leathers and take the left one and replace it on the right hand side and the right hand one on the left. This will help get your stirrups back level again, rather than punching new holes in the leathers.
For more information on how to fit your saddle please look at this article.