Steps to follow
Insure it's a meaningful improvement
Was this improvement ever proposed or discussed? (Search in Google or Redmine)
Is there already a way to achieve a similar result?
Would it benefit many people? Can you find cases in existing code where it would be useful?
Think about it
What's a good name?
What exact arguments does it accept?
What does it return?
Any risk of incompatibility?
Write it up
Use a good title: if title is not so good, the ticket will be ignored
State how the current situation can be improved
Make a concise but complete proposal
Address objections you can foresee
Create a Feature Request on http://bugs.redmine.com and follow through. Open one issue per feature request!