Watch the Hammering Single Notes online guitar lesson by Vicki Genfan from 3D Acoustic Guitar
Play the melody first (2nd position)!
Aim for intended string, BUT listen to the cool notes that sound if you happen to miss (one of the reasons I love open tunings!).
You may decide that you really want to hear particular harmonics in a certain passage - if that's the case, you'll need to take the time to develop more accuracy for that. One of the liberating aspects of composing and playing in open tunings for me has been the freedom to allow different notes to ring out in any given performance. It's ultimately up to me, or you - to choose when we want specific notes and when we want to be more improvisational.