It helps if you can pick up KUN and ON readings as you go while you are learning new vocabulary. Here are some useful tips for this:
・No KUN readings start with R-row kana (so any readings that do must be ON readings).
・ON readings are always only either 1 or 2 mora in length (so any that are 3 morae or longer must be KUN readings).
・ON readings with 2 morae can only end in one of the folloing 7 kana: い, う, き, く, ち, つ, or ん.
ON readings are from Old Chinese pronunciation of kanji. In Chinese each character's reading is a single syllable. However, in Old Chinese the readings can end in not just vowels and ん like nasal sounds, but also -K and -T consonant sounds. This is where the き, く, ち and つ endings are from.
There's other stuff like this which you pick up naturally for spotting whether a reading is likely to be KUN or ON. Along with knowledge of the basic rules about when to use KUN or ON readings, you should be able pick up and match readings to kanji fairly well, just from learning vocabulary. ^^
http://lingwiki.com/index.php?title=On_vs._Kun_readingsOctober 20, 2014 at 9:09am