What you avoid are:
1. Conditional constructions, of the 'if…then' kind, since they leave open the possibility that if a condition is not met, the task will not be done/completed. Such conditionals are often disguised:
"I should finish this by tomorrow IF the data arrive in time."
"IF I get the data THEN I will try to put a chart together"
Note that both the Active Voice and the Passive Voice are suitable:
"I will finish this by tomorrow at 5:00"
"This will be finished by tomorrow at 5:00"
2. Following an assertion with 'but', since it introduces a clause that contrasts with what was just said:
"I should finish this by tomorrow, but there is a lot to do."