Use parallel construction to make a strong point and create a smooth flow.
Examples

Incorrect: I was glad to be departing for Australia but I was nervous when I left my apartment.

Correct: I was glad to be departing for Australia but nervous to be leaving my apartment.

Incorrect: The system excels at tasks such as communicating with other computers, processing records, and mathematical calculations.

Correct: The system excels at tasks such as communicating with other computers, processing records, and calculating mathematical equations.
References
More information about this rule is available from the following sources.
Online Resources:  The Elements of Style: rule 15
Printed Resources: (see Books on Writing section)
 Strunk and White: 219
 Hacker: E1a,b