Question

What are some other verbal and nonverbal elements to consider?

What are ways to enhance credibility and why is this important?

Answer 1

I can't answer your first question because you haven't posted the verbal and nonverbal elements you've already considered.

Under what circumstances are you trying to enhance credibility?

Answer 2

eye contact

Answer 3

Here are some articles that might be helpful:

http://www.members.cox.net/dagershaw/lol/communicationDepths.html
http://www.members.cox.net/dagershaw/lol/CommunicationGenderBias.html
http://www.members.cox.net/dagershaw/lol/MessageAcross.html
http://www.members.cox.net/dagershaw/lol/StatusComm.html
http://www.members.cox.net/dagershaw/lol/InfluenceAntecedents.html
http://www.members.cox.net/dagershaw/lol/InfluenceMorePrinciples.html
http://www.members.cox.net/dagershaw/lol/InfluenceStillMore.html
http://www.members.cox.net/dagershaw/lol/Persuasion.html

I hope they help. Thanks for asking.