Here are a few things I've learned from reprocessing over the years, mostly as someone living off the land:
Make sure you go to a station that provides at least 50% reprocessing.
Get your Scrapmetal Processing to level V.
Large modules reprocess into a lot. One or two large modules is enough to build a frigate.
Certain modules reprocess into a lot more valuable minerals than others. The pink warp disruptor modules that even frigate sized Serpentis drop are worth almost 5 mil per piece.
Some modules, even small ones, may provide rare minerals like Megacyte. Dogtags often provide a couple rare minerals.
If a module reprocesses into 1 Megacyte, you won't get any after the 50% calculation. But, if you reprocess two of those modules, you will get 1. So it's better to reprocess in bulk that one at a time.
At most of my main stations I have a station container labeled Recycle Bin and I throw everything in there that I don't plan to use or sell.