What is the correct Syntax for "OR" condition inside "IF".?

Have an if condition like below

if ((listbox != "lhs") || (listbox != "prevnext"))

This is failing even when listbox is "lhs" or "prevnext" string.

Tried even below syntax but its failing

if ((listbox != "lhs" || listbox != "prevnext"))

Not sure of correct syntax for above condition.

Thanks in advance...!!!