Illustrator provides the following ways to preview how aspects of artwork will look when printed or viewed on the web or a mobile device:

Overprint Preview mode (View > Overprint Preview)

Provides an “ink preview” that approximates how blending, transparency, and overprinting will appear in color-separated output.

Pixel Preview mode (View > Pixel Preview)

Approximates how your artwork will appear when it is rasterized and viewed in a web browser.

Flattener Preview panel (Window > Flattener Preview)

Highlights areas of the artwork that meet certain criteria for flattening when saved or printed.

Soft-proofs

Approximate how your document’s colors will appear on a particular type of monitor or output device.

Anti-aliasing

Gives vector objects a smoother on‑screen appearance and provides a better idea of how vector artwork will look when printed on a PostScript® printer. Anti-aliasing is helpful because screen resolution is relatively limited, but vector artwork is often printed at a high resolution. To turn on anti-aliasing, choose Edit > Preferences > General (Windows) or Illustrator > Preferences > General (Mac OS), select Anti-aliased Artwork, and click OK.

Device Central (File > Device Central)

Lets you preview how your document will appear on a particular mobile phone or device.