Good colour management is vital to print design, and your screen is your first concern. People don't tend to see transparencies or colour prints very much these days, because so much is done digitally and there's so much soft-proofing. But if your monitor can't display colours correctly, and hasn't been calibrated and profiled, you're going to be starting from a bad place.
You do need to think about spending £600 to £700 on a screen, and the software and equipment to profile it, which is going to cost about £100 at the lowest level.
Setting up your software
If you haven't got your software set up correctly, you could destroy an image with one wrong keystroke. You need to have what is often called 'desktop colour management policy'. This might be given to you by your client or a printer, or you might say: this is the way I'm going to do it unless somebody else tells me differently.
Adobe Creative Suite lets you create a colour settings file: most versions of CS offer Europe Prepress 2 as a default, which is a good starting point. But while it's appropriate for printing on sheet-fed presses onto coated paper, as soon as you change paper or change the printing process, it's not going to be suitable.
Photoshop's colour profiles, for example, aren't the best you can get: you're better off bringing in your own profiles from organisations like the European Color Initiative.
Meeting client expectations
It's important to be very clear about what your clients are expecting you to do in terms of colour management. Are you making judgements about selection, corrections and re-touching, or are you simply providing a layout and design? Is the designer required to convert the files to CMYK? If you're given CMYK, should you be converting it to something more meaningful?
You also need to talk to your printer about colour management. You want them to be telling you to use this profile for that paper, or to give them the RGB files. Many printing companies have no pre-press: they just want the files. If they're not making sense or they say: "Oh no, just standard CMYK," then just don't use them.
For more on working with colour, check out How to choose a colour scheme