When I was learning, I had a great preceptor who would have me check first, and then she would re-check. I know, I know, those poor women! It took me a few, ok several, tries before I even FELT a cervix, but once I did, I had it down!
When I was teaching someone, and she was having a very difficult time, I drew her a picture, and then demonstrated with my hands the technique used. It helped.
Then there are those cool plastic charts that 2 years later I still use to double check dilation.
I have very large hands and long fingers and I have, at times, been able to get to a cervix when noone else could reach it. But really, if it is that high, you can pretty much bet that they aren't in labor. I once worked with a doc who wouldn't "dig" for it, and would just chart it as "high" in those situations.
One trick I learned was if the cervix is very high or posterior, make sure the bed is completely flat, and have the woman tilt her pelvis by putting closed fists under her buttocks.