Good writing is consistent writing, whether you’re writing a software manual or marketing copy.
If you end your sentences with the same mood, voice and tense that you start them with, the battle is already won. [Which rule did this sentence violate already? Answer at the end.]
If you start with active voice, end with active voice; or vice versa.
EXAMPLE: “I’d like to complain [ACTIVE] but I’m not allowed [PASSIVE] to criticize the coach.”
BETTER: “I’d like to complain [ACTIVE] but the club rules don’t allow [ACTIVE] me to criticize the coach.”
Stick to the same mood from one clause to another, or start a new sentence.
EXAMPLE: “Work hard [IMPERATIVE] and that’s how you’ll become successful [INDICATIVE].”
BETTER 1: “Work hard [IMPERATIVE] and achieve success [IMPERATIVE].”
BETTER 2: “Work hard [IMPERATIVE]. That’s the formula for success [INDICATIVE].”
Don’t go time-traveling from one clause to another.
EXAMPLE: “She was just minding [PAST] her business but this guy starts yelling [PRESENT] at her.”
BETTER: “She was just minding [PAST] her business but this guy started to yell [PAST] at her.”
(An excerpt from my book 101 Ways to Power-Up Your Writing )