I'm sure you'll have a number of favourite DJs, so listening to their technique is obviously a plus. What's worth remembering is that there are many different aspects to the art, all of which can be used on their own or together. Beatmixing is important, but not essential by any means (although as lardarz points out, it's fairly intuitive with a little practice). If you listen to DJs such as Mr Scruff or Gilles Peterson, you'll realise how little they beatmix - they use clever timing, but generally play the entire songs! Furthermore, they have a love of music - the most important thing of all :)
As far as pre-spend practice is concerned, your best bet is probably some mp3 software. I use 'Atomix mp3', 'cause I can't afford decks as yet, and it certainly gives you an insight into things. There are plenty of mp3 mixers downloadable for free, and for help and advice from those in the know, try iDJ (international DJ magazine).