Flight planning is very important part of any flight. If you go wrong during your flight planning stage one cannot possible think of the kinds of problems you are going to have once you have stepped into the cockpit. Although in real life, a dispatcher would have your plan really for you and you would meerly need to upload it via ACARS into your FMC life isn't always that easy for the virtual pilot and we dont have such luxuries which has left us with no option but to do it all ourselves! Here you'll find links to resources on the Internet, you may find usefull. In the Tutorial section you can find help/ideas as to how planning can be done.
Charts can be found on several sites on the net - both official and unofficial. The national aeronatic authorities do is some cases publish the charts on the net - some do not. I recommend you to check VATSIMs Pilots Resource Centre, where links to chartsproviders can be found.
Eurocontrol Flight Plan Assistant