I imported a piece of art into Illustrator and I want all parts of it to be equal and symmetrical. What would be the best way to start going about this?
Presuming the artwork is vector artwork, if it forms one half of the symmetrical appearance, you should be able to Object>Transform>Reflect a copy.
It may help helpers help you if you show a few images/screenshots.
I believe you may:
1) Duplicate the layer with the whole artwork and lock the original (layer/artwork), then work on the duplicate to
2) Delete either half, using a vertical line down the middle and Object>Path>Divide Objects Below and/or cutting the relevant objects (using Smart Guides which will say intersect when you are there), then
4) Recreate the faulty/missing parts at top and bottom.