I wait too long to change my rotary blade -- and I also sometimes don't close the blade.
I don't clean the machine after every project -- though I do try-- but when I do clean I am very thorough.
I forget to replace the needle in a timely manner.
This is not bad, but when I cut my fabric, the bulk is on the left -- I cut from right to left. If I don't use the shape cutter, I use two rulers when I cut the fabric.