I did see something on Lynda.com
https://www.lynda.com/OmniGraffle-training-tutorials/265-0.html
I can imagine that if there is enough demand, blogger MacSparky might be interested in making a video field guide for OmniGraffle. But you’d have to ask him that question.
Even though we have a tool such as OmniGraffle to design charts, it also helps to have a background in design and graphic art.
There are aa few youtube videos scattered. Some are for older versions of OmniGraffle but the concepts should still be there for you.
https://www.youtube.com/results?search_query=omnigraffle+tutorial
And the best way to learn is to have a project that requires OmniGraffle and do it yourself. Learning on the job is often a painful birthing process but sometimes need to get you where you want to go.
