For booking tickets, hotels, or tables, these two are almost always interchangeable. 预订 (yùdìng) has the character `预 (yù)`, which means “in advance,” so it slightly emphasizes the “pre-booking” aspect. However, in practice, both `订票` and `预订票` are correct and mean the same thing. 订 is slightly more common and versatile (e.g., you can only say `订婚`, not `预订婚`).