Like Saruda said, learn Hiragana and Katakana really early.
At most, I'd say it takes you about 4 days to somewhat have them in your head.
These signs show up the most in Japanese language (well, Hiragana that is) and the earlier you can seriously read them, the better.
A method I find very useful, is the one of Heisig's "Remember the Kanji".
It helps you remember the Kanji, by making little stories for with each part of a Kanji.
It only helps you at knowing the english meaning of a word though, but you can practice the Japanese readings, getting untranslated stuff, like eroge (where yo