You know the feeling... 

A new table from Ikea (Lack) and a tiled floor that is not level :-(

Here's the solution: the Ikea Lack stabilizer. 
Print 4 feet, if you use ABS your table is also protected against water when cleaning the floor.
See which leg is not stable. 
Print one or more of the inserts and place them in the printed foot under the "bad" leg. 

Your table is stable and also looks much cooler.

Ikea lack table feet = 51 x 51 mm.
If you have another table with another dimension, let me know, I'll design it for you.

I printed mine at 100% infill to make sure they are sturdy.