There are certain days and times that are better to fly on than other flights for a few reasons. If you are sensitive to airplane turbulence, morning flights would be better for you. As weird as it may sound, this is because morning flights mean it's not as hot out. Heating from below creates unstable conditions like storms, winds, and bumpy flying, which directly leads to high turbulence. Best to only book during the morning then.
If you're looking for cheaper flight fares, then it's best to look for flights on certain days. International flights are usually cheapest on weekdays versus the weekend.