I guess the route depends where you're starting from ! But for what it's worth, I did it (about 2 years ago) as follows :-
Leeds -> Munster Osnabruck -> Prague (Ruzyne) -> Budapest (Ferihegy)
Coming back was similar, but for various reasons we landed in Karlovy Vary instead of Prague, and chucked in a quick stop at Norwich before returning to Leeds.
My routes had longish sea crossings, so you need to decide how you feel about that. If you're not keen, then obviously you'll have to route via Dover/France/etc.
The most direct route from Prague to Budapest would have meant overflying Slovakia, but I couldn't get either decent charts nor advice no matter where I looked. I rang the Slovakian CAA to ask about VFR routes (to avoid the military zones etc), but they really didn't want to know (or possibly didn't understand me). Not wanting to get shot down, I decided a quick (and not huge) detour was in order, and went via Austrian airspace. They seemed confused to have me, but it all worked out eventually.
One thing to note is that when filing plans to cross from Germany into Check airspace (and vice-versa), they insisted we gave them a precise location of transit : so we just picked out a town or village from the chart and included that on the FPL, and everyone seemed happy (except the Autrian ATCOs, who seemed universally miserable, but hey-ho ... !)
As to advice, well ... the usual stuff really for flying in Europe : check opening times/fuel availability/handling requirements etc VERY carefully (fax or email is a good idea), don't forget that many places do not accept credit cards for fuel, so you need cash (or a fuel card, eg BP is reasonably widely accepted). If you're going VFR, make sure you understand the actual rules for each country !
The airport at Budapest is straight forward enough, just make sure you book handling in advance, and be prepared to be on your toes - it's a busy spot these days. They were manically busy when we got there (Grand Prix was in town) but they gave us a really good service at a pretty reasonable price.
As you get further East, the quality of spoken English on the radio can become a little ... variable, so you need to try and be alert for (eg) VRP names and locations etc.
Other than that, fill yer boots - it's a pretty nice place to visit - enjoy !
FF
