As much as slides, vibrato and mwah are great fun and are pretty much the de facto, trademarks of fretless, also set some time aside avoiding these and try and make it sound like a fretted bass (accurate fingering, using the fingertips, without vibrato). The ability to move between these techniques means that when you break out those trademark, fretless tones, they’ll stand out as features, rather than being full on, all the time.