Another valuable article from Tulsa World of Gymnastics on the neglected, if not forgotten, forward hip circle on bars.
A waste of time? Or a valuable progression for kip?
… Now, the crucial part: timing. To correctly do a front hip circle, you need to keep your body extended as you lean forward until you are about to reach horizontal. Now is the time to put your stomach muscles in action. As quickly as you can, snap your body from the extended position to a pike. (Many beginning gymnasts exaggerate this extended-to-pike snap — and this is okay — but as you become more comfortable with the skill, you can start from a hollow body position and go to the pike.)
Be sure that you think about bringing your chest to your legs, rather than letting your legs drop as you bend your body. Making this mistake will result in a decrease in how much power you get going around the bar. …
See the rest of the article – Tulsa World of Gymnastics

More articles like this in their Gymnastics Tips for Gymnasts and Coaches section.
Personally, I like forward hip circles. They are not super important progressions. (Most boys would do very few.) But it’s a good challenge and supplement for girls learning kip. If you have them in compulsory routines in your region, count yourself lucky.

… Now, the crucial part: timing. To correctly do a front hip circle, you need to keep your body extended as you lean forward until you are about to reach horizontal. Now is the time to put your stomach muscles in action. As quickly as you can, snap your body from the extended position to a pike. (Many beginning gymnasts exaggerate this extended-to-pike snap — and this is okay — but as you become more comfortable with the skill, you can start from a hollow body position and go to the pike.)