Lucky, a strong understanding of the types of doubling out there that are not value adding, such as machine doubling, will make the others become much more obvious. Coppercoins website, http://coppercoins.com/
, has been a great help to me. I would also suggest his book, "Looking through Lincoln Cents". He does an excellent job of describing all of the primary known doublings with very descriptive pics.
I would say that once you start to see machine doubling for what it is, true die doubling will become fairly obvious. Machine doubling is the one that throws most everyone and it is very prevalent. I am willing to bet that if I grab a handful of 1950 and 1960 cents, I can find machine doubling on close to a third of them. Anyway, keep studying and I would suggest getting a scope. I finally invested in one recently and I am amazed how much more I see.