In addition to a good textbook (check your local public library) I'd make the following suggestion.

PALASM sometimes has a manual with it that explains an awful lot about logic design, state machines, etc, and it nicely reduces logic for you. It's got a functional (no timing) simulator to help you find those places where you've got an extra inversion, or lack one ... but it doesn't resolve races or metastability for you. If you can find a reasonably complete version, it's free, but the manual is pretty hard to find. The intermediate logic handling that you find in ModelSim, while ModelSim accepts ABEL input, is syntactically compatible with PALASM.

I've found, here and there, bits of logic reduction, translation of truth tables to POS or SOP format, for logic reduction, Karnaugh maps, etc, on the www that are as good as the best texts I've seen and used.

Be very careful, but if you find a good VHDL text that you can read (check your local library) then see if you can buy the latest version somewhere. Too many texts emphasize the "how" and forget about "why."

RE