So what you want to do to achieve the appropriate tone is use a clean tone with midrange and treble. Roll off the bass, but keep it warm, not too shrill. A lot of the tone comes from where you pick the string as well. The most important thing is the reverb, and when I say reverb I mean lots of it. A good way to know when you're getting close is when the sound starts to bubble a little...that gives surf guitar it's "wavy" vibe!