Writing logically basically involves writing in a manner in which there is no other way of perceiving the written thing.
“There is no way to go faster than the speed of light.”
In this sentence there is more than one possible meaning. The person could be talking entirely in the literal sense that it is simply impossible in the universe no matter the means, to travel at a speed greater than the speed of light, or they might instead mean that there is currently no means by which a person might travel faster than light, but that it may be that it is still unknown whether or not this is possible.
Writing logically as a concept eliminates this possibility for secondary or multiple meanings. Writing logically the statement might be something like the following:
“Travelling faster than the speed of light is currently not plausible with humanity’s present technology.”