Conference proceeding after journal article
Depending on the particulars of your situation, there are three paths I am aware of for presentation at a conference:


Some conferences have begun to offer "journal first" submission options that explicitly welcome the presentation of an article that has already been presented in a journal.  For these, one prepares a short precis of the article for review and it is explicitly understood that this has already been published.
If you have some new results, you can certainly write a conference paper on these new results as an incremental advance over the prior work. Here, you simply focus on the new results just as you would for any publication building on prior work.  The only question is whether the new results will be considered significant enough for separate publication by your reviewers.
Finally, some conferences don't involve peer-reviewed articles at all, but just have one-paragraph abstracts submitted as "applications to speak", in which case figures and self-plagiarism don't enter into the question at all, since the abstract is not a publication in any meaningful sense.


From what you have written, it sounds like the first or second path would apply for your needs.