Ciff is right start by making sure you have a clean print bed and add something to the surface to aid adhesion.Glass beds are great because they are flat but have no texture to gab the extruded filament (unless they are frosted)so often need some help. one cheap solution we use is to clamp a thin 1mm piece of Tufnol (Garalite in USA) to the glass and print on that. lightly sand the surface and it ready to go. We don't use any coating on that surface for PLA or Nylon, but for ABS we use ABS Milk ( 10% abs dissolved in Acetone) and a smear of PVA stick (Prit , Elmers) for PET-G.Thin Tufnol is cheap About 80p for a 325 x325 piece for the Ender 3 and if a job sticks hard to the surface gently bending the tufnol sheet always releases it.