OK so my advice to Beholders the world over is to make sure they realise just how crazy powerful their rays can be.
For example telekinesis is actually really useful: you can hurl a large number of greatswords at a party; you can hurl a party member or minion at someone else; you can disarm that pesky rogue or divine focusing cleric or wand wielding wizard.
Beholders should always make use of their flight ability:
use grease (spell or mundane) on the floor to hamper those pesky heroes.
or just hover over a pit trap and wait for the fighter to move up to you and trigger it. this is especially effective if you pretend to be backed into a corner or floating around the corner of a corridor forcing the PCs to come at you
cheer up beholders you have a wide array of attack options, just remember that you can move in 3D and perform hit and run tactics in a lair that you design and if all goes to hell in a handbasket then just send in the charmed cannon fodder and retreat.