There's a really good and easy to read textbook on botany and how to tell the families apart by inspection/ dissection called "Name that Flower" by Clarke and Lee. I recommend it highly. It's probably about $20-30. It's only small, and it's very clear. I'll often rip a flower up to have a look if I'm not sure. Lots of the defining clues are really easy once you know them - e.g. Lamiaceae family (mint family, mint bushes, lavender, sage etc) have square stems in cross section and aromatic leaves. Rose family has five of everything in the flower. Once you get the big clues it's easy to track things down, because you know where to look.