Tough trying to tell a mature ewe from a baby ram. This will cause you to hesitate more than anything. They are very susceptible to the lost wallet stalk, but, can tell by your body language when you are ready to shoot. Work on trying to be nonchalant. I found later in the season more enjoyable, spending time in sheep country watching the rams spar and having to walk by 180" rams to try and kill a ewe....priceless.
Have fun, learn sheep habits, this will payoff in spades when you draw your ram tag.