Some countries and areas are harder than others. Try to learn the symbols, if any, that each country uses in certain periods.
Great Britain has the Queen's bust on modern stamps or Japan has the Chrysanthemum, currencies used, abbreviations for currencies, styles of stamps perhaps also.
Some French and British and other European countries have issued similar series of stamps for their colonies which are pictured in the front of the catalogue usually.
All kinds of tricks like that, and as you learn one then that area or country will become easier to find next time.
Learn bits of foreign languages as you go along also. Use Google translate or other internet translaters.
If you think they are from a certain country try
ebay or Delcampe or Google and search through the years or eras you think they might have come from.
Learn to read postmarks and check the dates for which year they were used. This won't work sometimes as stamps were kept and used for years after sometimes but it gives you a start point.
You cannot know everything there is to know. The best thing to do is have books or computer databases (like Rod's) or knowledge bases like SCF to query. That is a smart move.
The more you get to know, the more there is to know, but when you get to a certain point it all slows down and you know enough to know where to look for an answer or where to ask a question. That's when it all becomes easy.
There is a book called Outliers that talks about how people become so good at different things that they do. It all comes down to how much actual time you have spent doing something and had practice at. To be Good you need 4000 hours. To be able to teach something you need 8000 hours. To be in the master class of anything you need 10,000 hours. Kind of gives you a perspective doesn't it?
When you start out at something and have a few hours or maybe 10 hours in at doing something and you get frustrated at your lack of progress and how hard it all is just remember the 10,000 hour rule. At 10 hours there is no way you are even close to the 10,000 hour mark so just relax and enjoy the ride. Simple.