The text height and other size settings for dimensions have to suit to the size of the drawn object, units and intended (printing) scale. So if it's a mechanical part in mm, let's say 250mm long and to be printed in 1:1, the preset values in options - current drawing preferences - dimensions might do it. But if it's a building, in meters, to be printed in scale 1:100, you will have to change these settings. With 'general scale' you can modify all the values (except 'fixed length'), so you don't have to change all the individual values for a different scale. Also ensure a paper size is set.
I had the same problem, finally figured it out but also wasted a lot of time. I've been messing with Librecad for a couple of years and have yet to get it to be useful. I just installed 2.1 (linux) hoping it was fixed, it's different but still not useful. I'm a toolmaker and use CAD every day for the last 30 years so I'm not a newbie but I prefer Linux and wish there was a usable Linux 2D CAD application, Librecad is not it.