The Rough Guide to First-Time Europe is an excellent reference. I was not going to be travelling for as long as three - six months, only one, but I did find much of the advice very useful as a starting point. This was my first lone travel experience and quite frankly I didn't know where to start in some areas. Such as, how much of what to pack and what to leave, I mean really leave behind! I will tell you that I used everything that I brought and did not find anything lacking. I will refer to this guide again for future, longer trips, so I would recommend it even as a refresher reference for more experienced travellers. Everything from daily spending advice based on your budget to health and safety is very helpful. Also the country profiles are in good detail. If you have parents to convince that this is a good idea, it even has advice on how to approach them!
All in all an excellent and to the point reference guide!