Whenever possible, I plan my borders to be cut lengthwise. It's not a waste for me. I still use the rest of the fabric. It just requires a bit more thinking in order to plan how to cut the other pieces. I never have a problem with wavy borders, which is a bonus.
I don't have a lot of space to work, so I try to spread out on the kitchen table with my fabric. My largest cutting board is 18x36, so I have to keep sliding it down as I go. I fold up the fabric and try to keep the lines on the ruler lined up with the fold. I just take my time and cut slowly.