You can find options for the project-wide appearance and position of glissando lines on the Glissando Lines page in Engraving Options.
The options on the Glissando Lines page allow you to change the style, appearance, and thickness of glissando lines. You can also set precise positions for the endpoints of glissando lines relative to noteheads.
There are musical examples for many options to demonstrate how they affect the appearance of your music.