| As a general rule I've found its best to keep my thumb opposite my middle finger. I feel this keeps my whole hand more in line which will become more important if you start using a fourth finger. I also keep my thumb in the middle of the back of the neck, to get a better reach. But if you find your method more comfortable, stick with it!
A good exercise to get yourself used to the fourth finger could be simply a 1,2,3,4 exercise (where 1 is your index, 2 your middle finger, etc). Or you could practice scales in 1 position. A bit of advice - doing the 1234 exercise could be a strain considering you're not used to this, so start doing it higher up the neck, say the 7th fret, and work your way up to the 1st slowly (over a course of days). You may not need to do this at all though, depending on your hand size.
When you feel you've got it down, maybe have a go at 'Money' by Pink Floyd using your 4th finger. |