Ive found over the years is get a bass that you really feel comfortable with. Some fretless basses ive played & owned you can just never get the intonation right ever & some feel like you can never get a note wrong. Status basses make killer fretless basses like that and so do Wal. But though they're best for me they might not be for you. I think with fretless you seriously need to make friends with your bass. You'll know when you find it !
Another tip is always make sure you can hear yourself properly & if you're playing with a band & especially when the PA guy turns the front of house up, its so easy to lose your sound/monitoring and sound like a t__t.
Try and play with other musicians as much as you can too, its so easy to sound in tune on your own but then when your playing with others its totally different.
Also trust yourself its sometimes better not to look at what your doing.
That last bit will make more sense once you get going. Good luck ; )