I learnt them through all of school but have hardly practised since, thanks to starting Mandarin and Japanese at uni D: This also means my resources were mostly high-school textbooks.
One bit of advice that I wish I'd had, is to learn a few basic affixes and their general effects quite early. If you haven't already looked at this, it makes vocabulary a lot easier to learn (instead of facing a wall of verbs starting with ber- and me- and trying to memorise them!), allows you to look things up in the dictionary, lets you experiment with 'creating' new words from base words you know, and allows you to figure out the basic parts of speech. If you have been using a dictionary you've probably found about about the affixes already but in case you haven't here is a rather comprehensive site: http://www.indodic.com/affixeng.html
. There is a better all-round site here: http://www.seasite.niu.edu/indonesian/tatabahasa/
If that's too in-depth here are some sweeping generalisations of the major affixes:
ber- prefix means an intransitive verb
me- (mem-, meng-, men- etc) prefix means a transitive verb
di- prefix is the object-focus version of me- prefix
-kan suffix can go along with me-/di- prefixes, often causative or benefactive
pe- prefix makes a noun, often someone/something who "does" the base word
-an suffix also makes a noun
pe- -an affixes are also nouns, often more general or abstract
ke- -an affixes do all kinds of things
I still have all my textbooks and notes though, so if you want any advice or even to practise feel free to PM me. I was basically fluent for a while but... er... six months of no practice was too long D: Also, I really apologise if this is too much information/not enough/incoherent/etc. It is probably too late at night for me.