Reporting part-time earnings while on benefits - any advice?

My hours change every week at my new part-time job and I am afraid of reporting wrongly. Any experience at all would help. The form asks for gross earnings, which I do not see until later. Who can I ask without risking my claim?

Report honestly and keep your stubs. An honest small error is much easier to fix than a missing report.

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.