General:
* Candid
* Frank
* Honest
* Sincere
* Simple
* Direct
* Explicit
* Clear
* Uncomplicated
Specific to communication:
* Forthright
* Blunt
* Outspoken
* To the point
Specific to task or process:
* Easy
* Effortless
* Uncomplicated
* Simple
* Basic
Specific to personality:
* Down-to-earth
* Practical
* No-nonsense
The best word to use will depend on the specific situation and the nuance you want to convey.