The best way is to associate the noun class patterns with how you make the word plural. So, for example, for object infixes associate ji/ma class (gari, magari) with li- and ya-. Associate m/mi (mti, miti) with u- and i-. That approach covers most classes: ji/ma, m/wa, m/mi, and ki/vi. After that, the remain two classes - U an N are easy to distinguish because U nouns almost always start with U, anything else is a 99% change of being N class. Bahati nzuri!!