This was also my first month using OPK's so no expert either Im afraid, however I did start testing very early (good job really as O'ed very early).
I found the following results with mine:
CD 9 - no line
CD 10 - visable line, but very faint
CD 11 - slightly darker, but still faint
CD 12 - tested twice - 1st result getting darker, 2nd result in the evening very dark, although still not quite as dark as the control line
CD 13 - back to a faint line again.
According to the above I potentially ovulated morning of CD 13, which would fit with the pains I was having!
The 2nd line should show darker or as dark as the control line (depending on the brand), and you should ovulate within 12 - 36 hours of seeing the dark line!
I think in order to ensure you see your LH surge (when the dark line appears), you need to test at least twice a day, starting as early in your cycle as necessary otherwise it would be so easy to miss the surge and not have a clue.
I have just ordered a basal thermometre so I can start charting next month, as I really want to know what my body is doing!
Hope that helps a little!!