Use a bunch of terrain / pillars etc so movement and LOS are interesting.
Add a couple other bad guys into the fight so it's not just one BBEG vs the whole party.
I always use the eye beams sequentially rather (than randomly).
And give it a ton of insane hyper-confident personality.

In a recent AL adventure there was a room w/ a beholder and a couple helmed horrors (reskinned as undead so they function in the antimagic beam just fine), the room had a bunch of wormhole portals that created crazy LOS and was shaped in tiers so the PCs were always climbing up a 10' tier, or jumping down or falling, etc. It was pretty interesting.

Beholders are as fun as you make them.