Bus 17/17A/17B (£5, 30 minutes, half-hourly Monday to Saturday, hourly Sunday) The quickest route to Penzance, via Lelant and Marazion.
Bus 16/16A (£5, hourly Monday to Saturday) An alternative route to Penzance; bus 16A travels via Zennor and the Gurnard's Head pub, while bus 16 goes via Halsetown, Ludgvan and Gulval.
The branch train line from St Ives is worth taking just for the coastal views.
Trains shuttle between St Ives train station via Lelant to St Erth (£3, 14 minutes, half-hourly) where you can catch connections along the Penzance–London Paddington main line.
Parking is one of the main headaches for anyone planning on visiting St Ives: traffic can be very bad in summer, and attempting to drive through the town centre is a recipe for holiday nightmares.
The largest car park by far is Trenwith, a brisk uphill walk from town; it's usually the likeliest to have spaces in summer.
Another useful alternative worth considering is to use the park-and-ride system by leaving your car at St Erth or Lelant stations, and then catching the scenic St Ives train line into town.