First of all, you need to really get to know each and every part of speech. Meaning: you should learn it, and practice it ? a lot. Then it becomes easy. It's like learning to drive a car ? it's usually not easy at first.
So, as an example, you could study the part of speech, let's say the ADJECTIVE. You learn that it is a word that describes a person or a thing. You look at the examples, and make up some examples of your own. Then you could go over ten or so sentences, and circle the adjectives. I think you will discover that you can now identify it rather easily by only seeing the sentence :)
It is not a shortcut but it is a rather sure route?