Grouping the Lojban root words is a very worthwhile way of acquiring usable vocabulary. One way of doing this is the Lojban Thesaurus grouping.
Another, more controversial, is to sort according to the number of sumti each takes, whether one, two, three, four, or five:
The sumlairdunkemgimgri 'groups of gismu of equal quantity of sumtis'--
1. narju xarju ('orange pig')
2. grusi gunse ('gray goose')
3. crino cinfo ('green lion')
4. blabi smani ('white monkey')
5. nukni jukni ('magenta spider')
Within each group there would be further subdivisions.