This is how I get 90%+ of my photos geotagged:
1. take photo
2. lock phone
3. put phone in pocket
I do not exit the camera application or close the lens cover.
I believe that even after the camera app goes into standby it continues to look for a gps lock to tag the photo. If you close the camera app the phone stops trying to apply geotags.
However, leaving the camera app running has its drawbacks. After the gps location has been acquired and the photo has been tagged, the camera app seems to keep the gps lock thus draining battery. I came to the conclusion that the gps lock still runs when the camera is in standy because when I take the camera out of standby the gps position is immediately known (pushpin icon not crossed out).
I only use this technique when I'm in a lots-of-photos-today situation.
Regarding battery drain, I got 10 hours (full charge to dead) at Legoland while snapping away all day (sixty images and fifteen cumulative minutes of video), push-email running in background (profimail) and a two-minute phone call.
No doubt battery life will differ between theme parks.