I tend to agree with Matt. Start with a simple, 1/72nd scale kit of 'fighter' size - something fairly simple, say a Spitfire, just to get accustomed to the assembly technique etc. Don't worry too much about detail painting, extra detail etc, this will come later.
In fact, even if you make a real mess of it, the main thing is you will have learned something. The basics are knowing how to assemble, and adjust and set things such as the wing dihedral, how to deal with seams and joint lines and so on.
Once you are fairly happy with the basics, then move on to perhaps 1/48th scale, with more detail;, and concentrate a little more on getting the detail in the kit right.
If you feel that 1/72nd scale is a little small to handle, then all of the above still stands - just keep to the same type of kit (eg Spitfire), but in 1/48th scale, and preferably a lower cost version; the Revell kit mentioned by Wojtek being ideal. You don't have to spend a small fortune to make a good model !