Outside of just learning how to use the software (which I'm still doing!), the things I've struggled with the most are mixing and mastering. I've recorded a bunch of stuff that when played back to back all sounds completely different in terms of levels and mix, and sounds inconsistent when I play it on different stereos.
One book I picked up called
Mastering Audio: The Art and the Science speaks to a lot of this, and gives some great suggestions for ear training, leveling (and how to use the various meters), equalization, manipulating dynamic range (right and wrong ways to use compression, etc...), and lotsa other good tid-bits. Its written very well, and really explains a lot of the basics in clear terms. Excellent book, and highly recommended!
I also benefited from these white-papers that speak to some of those concepts - good reads as well:
Mixdowns for BeginnersGuide to Mastering for BeginnersLeveling, meters, and many other topics along the way...As far as software and computer stuff goes, two things that I've picked up that I find helpful are:
Spectrasonics Stylus RMX - this is a plug-in of sorts that has umpteen-zillion pre-fab drum loops. A lot of the base package is geared towards electronic music, but there's add on discs for real sampled drum loops (I think its Gregg Bissonette playing, IIRC). This is really nice to use when developing out an idea, as you don't have to sit there and toil over drum programming. I usually start with this, and then go back after and revisit the drum tracks - or sometimes bounce them thru outboard gear for processing, like Harry was describing. One tip- if you buy the base package, they send you a deal at the end of the year where you can buy all five add on discs for $99 (at least they did for me the past two years). Usually those are $99/ea. Of course- a real drummer is always best, but this drinks less beer
Universal Audio UAD-1 - This card gives you a dedicated processor for plugin effects. I got the UAD-1e Express Pak when they were blowing it out for $99 (after the release of its successor), and it comes with really nice EQ, comp/limiter, reverb, a guitar processor type deal. I've never had a prob with processing power using the plugins I have in Cubase, but these UA plugins just sound soooo much better to me. Its worth it just to have them. You can still find the cards cheap on Ebay. Just note that UAD-1 requies a PCI slot, and UAD-1e requires a PCIe slot in your 'puter.
All I need now is time to use the stuff
Good luck, and post some tunes!