I posted the following very recently in response to a call on whether or not to play unlined:
Welcome to the (un)marked side! I mindlessly bought a cheap bass on eBay assuming it was fretted and it was not only fret-less, but unlined too. I had a choice - offload it, or play it. So I set to learn to play it.
Background - I had around eight years of fretted playing and a bit of lined fretless along the way. So I wasn't entirely unused to not having the 'tin ladder'.
First thing I did was check the position of the side dots - the only guide on my Revelation - to ensure they're actually on the notes, not in between as on fretted and many lined fretless. You are stuffed if the dots aren't on the note. To do this I carefully tuned the bass then then placed my finger in line with the side dots and checked the tuning in each case with a good tuner. In my case all my side dots were on the nose, except the 12th fret dots which were a centimetre adrift: really odd. I had Bass Gallery in Camden black out the existing 12th dots and drill and mark new ones on the note.
Then I started playing, simple tunes for a while, where possible using G, C, D, A, etc, notes that are in line with one of the side dots (1,3,5,7.etc), looking to see where I placed the note but also listening to the result, and occasionally using the tuner to check I was in the right place.
This all came much easier than I expected pretty much from the get-go. The key is starting to really listen and think with your ears, not just plonking your finger behind a fret.
Then I started on the 'inbetween' notes; that is notes like F# (2nd fret E), C# (4th fret A), etc which fall between the side dots. I tried to work out carefully where these notes should be, remembering that there are two notes between the nut and the third fret mark, and again each side of the 12th fret. And also that the gaps between notes get smaller as you go higher up the board.
I found that being slightly out doesn't matter so much, providing your rhythm is good, even more so if you're playing with a band or track. But finger position does get more and more critical the higher you go. It took me just hours to master the note positions up to the 9th fret marker; months to get the hang of 'frets' above the 12th, where the space between notes is much smaller. So playing low down is pretty easy, chords or soloing high up is really difficult without guide marks - I keep a lined fretless for the latter activities.
In summary I'd offer five advices: 1/ don't let it terrify you, it's not as hard as you think 2/ spend a little time at first working out where notes are and consciously practice finding them, looking at first, then looking away after a while. 3/ Correct yourself when you get it wrong then practice the corrected move - don't get into the habit of guessing a position and then adjusting your finger, you'll do it all the time. 4/ Start simple and slow at first and then speed up. 5/ learn to trust your ears and fingers to get it right if you give them a chance. You can use chalk or other temporary lines to help but it's just prolonging the conversion process.
I didn't have a book, or video, just worked it out for myself. I'm pretty thick, even challenged, at music and I could do it. I hold down the bass chair in a good regional blues and R&B band playing U/L FL all the time and haven't been sacked yet.
Come back if you need more.