I'll just start off by saying I'm not exactly new to Japanese but I'm still learning the kindergarten equivalent of what native speakers learn. I've mastered Hiragana and Katakana and am using Genki to learn my grammar and Kanji. One thing it fleetingly explains and that I'm still confused about is the difference between On and Kun readings. I understand that On is for the Chinese benefit and the Kun is the reading the native speakers made for their speaking, but when making compound Kanji, there doesn't seem to be a pattern between the usage of On or Kun. It says that On is also the "sound element" and Kun is the "meaning element", so how am I supposed to know the difference between when to use either one??
Experience is the best teacher.
Here are some general tips that might make reading kanji easier:
- For pairs of kanji, you will most likely use the on'yomi.
This is not a hard rule. Kanji that come in pairs of 3 or more also apply in this case, but sometimes the way you parse the words will also dictate the reading. You may also encounter situations where one kanji uses the on'yomi and the other uses the kun'yomi. Experience reading these characters will give you the best feel for how it will work.
- Kanji that is proceeded and followed by kana will most likely use the kun'yomi.
Once again, there are exceptions to this rule too. Since kanji was adapted from Chinese, some Chinese words became part of the Japanese vocabulary. These Chinese cognates, while not the only exception, are the main exception to this rule. Once again, the more experience you have with a character, the easier it is to read.
- There is no substitute for experience.
Practice Practice Practice. You can never get proficient at anything without practice. The same definitely applies to kanji. The more experience you can get under your belt, the better prepared you will be when you encounter a new word using kanji you recognize.
In general, its determined by whether or not there's hiragana attached... This is a pretty good place to start: