If you don't come across it often, you are bound to forget it.
I personally use flashcards, which helps me remember almost every word I learn, but this takes a lot of time.
If I were you though, I'd still use flashcards a bit particularly with words you want to remember but probably won't see often.
I use CueCard [
http://download.cnet.com/CueCard/3000-2051_4-10075304.html ] which is a very simple Q&A flashcard program. You could make the question the word you want to remember and the answer its meaning or Chinese translation. You can even use pictures and sounds for the questions or answers.
If you don't want to just see the word on the screen, you could use an audio file for the word. Either record it yourself, or take it from the internet. I use this add-on for Firefox [
https://addons.mozilla.org/en-US/firefox/addon/flashgot ] and then find a word from [
http://dictionary.reference.com ], then it's just one click to automatically download the audio file of the word being pronounced.