First thing for newbies to practice I would say is to say to themselves I'm a Whistle player instead of saying I’m a newbie. A small psychological point maybe, but it should install a bit of much needed confidence right away. Practice not making comparisons with your playing ability with other players, a lot of new players do. It’s a personal journey of discovery, enjoyment and experimenting for many years I hope.
Everybody learns differently, at different times. Practice what you like, there’s no exam or grading for this. Challenge yourself to learn the difficult bits.
Good tone comes from good breathing, phrasing etc, regardless of what particular ornamentation you use, the tune has to sound musical. Listen intensely, play with other musicians as much as possible, this helps to gain confidence. If there are no musicians around, play along with MP3’s or whatever, try playing along with tunes on clips and snips.
While I would advocate practising slowly, I would also advocate listening at speed and learning at speed as much as possible.
Given the choice, I would rather learn to read music, than learn any tab or ABC notation. Only reason being is that it makes much more music acessible to you. Either way, every musician learns by ear.
Practice with as many whistles as you like, just make it musical.
Thats enough for now I think
Cheers pkev