Trespass, we have done this a few times and have tried the following variation
1) Drive to Palma, find somewhere to park and make way to the station and board train, once in Soller, take tram to puerto Soller ..... reverse journey home
2) Drive to Inca, get train to inca, walk 2 mins to station next door and get train to soller then as 1 above
3) Drive to Soller, leave car at soller, take train to Palma ...... spend most of the day, including lunch in Plaza Major, in Palma, train bacl to Soller ( less crowds on train because they are all going the other way )
All have their merits, options 2 and 3 certainly the easiest
For us the best bit is the train journey, it's magical .... really great if you spend some time standing outside on the little platforms at either end of the carriages.
If you have never been to Soller or Puerto soller via the tram, then option 2 wins hands down ..... if you don't necessarily want to see Soller or Puerto soller then option 3 is a great option.
Have also heard of poeple who have taken Bus to Palma, then train to Soller, tram to Puerto soller then bus back to PP via the mountains ..........
Whatever you decide, do make sure you get to go on this train , it if fab