I Went backpacking all through Europe, and a few other adjacent countries, about 5 years ago and I am currently in my second trip now; just been through Nederlands, Belgium, Spain, Portugal - and am currently in Greece Macedonia. If you can go to Spain, I recommend it very highly - it's one of my favourite places in the world.
Despite my own experiences, I don't really have very much to offer. I see you're going by yourself - if you're the introverted type, travel can be lonely experience if you don't make efforts to meet people. If you're staying at hostels, don't be afraid to have a drink and chat with other travelers - even if you're not a big drinker.
Also, don't be afraid to talk to the locals - if you find the opportunity to make friends with the people who live in these countries (as opposed to just other travellers) you will turn your travels into a very special experience indeed. There is only so much you can experience as a visitor to a foreign country - the 'natives' are where it's at.
It's a good idea to learn the basic phrases in every country you go to, even though most people you come across in the countries you have mentioned will speak excellent English - imo, it's just excellent common courtesy. Courteous phrases are things like: hello, goodbye, please, thank you very much, I'm sorry, I don't understand, I don't speak X, do you speak X? - it will make your trip a much more rewarding experience, and locals will always appreciate the gesture.
Not sure if you are trying to do your trip on a budget, but you can do free walking tours in pretty much every major city in Europe - the tour guides rely on tips; you tip whatever you think the tour was worth. If you thought the tour was no good, then there is no pressure obligation to pay at all; they understand that everyone has their bugets.
I highly recommend these tours - the guides will take you around to all the major landmarks, give adequate -and often entertaining- details about each site and will often show you a few spots you won't read about in any lonelyplanet, wikitravel or tripadvisor guide.
SANDEMANs NEW Europe - Birthplace of the Free Tour are the best - check the website, but you will find them with red umbrellas in the main square of many cities at certain times of the day. Don't miss the free walking tours in Germany, especially Munich and Berlin - second world war history is both horrific and fascinating.
The organisation I linked, also do bar hopping tours at night, which I imagine would be a good place to meet others; but bars aren't really my thing, so I've never done it myself.
If you find the opportunity whilst in Switzerland to visit Geneva, you should go to CERN - the home of the hadron collider. You can do a free tour of the facility, but you need to register on their website in advance.
If you're on a budget, try to cook your own food as much as possible and buy food in supermarkets; this also means it makes it a bit more special if you decide to dine out or have lunch somewhere. Also, you can usually get falafel wraps, kebabs and shawarmas for about 3.50 to 4 euro in most countries.
Drink tap water wherever you can, you will save tonnes of money from buying bottled water.
Don't even think about trying to cross any borders with contraband of any kind - I know I don't need to say this (nexians are smart cookies), but it's easy to fall into complacency whilst traveling around. Same goes for buying any contraband - just be careful, and go with your instincts.
If you're looking at hostels to stay - check for good reviews; don't just look at the star ratings/percentage. There are lots of fake reviews - read the reviews and cross reference the common complaints and remember that most people don't write reviews at all. Most importantly, don't stay anywhere that doesn't have secure lockers for you to store your valuables. Don't stay anywhere that wants to keep hold of your passport - they can scan it by all means, they can hold onto your drivers licence instead, a monetary deposit even - but at the end of the day, your passport is not even your property and if anything happens to it, you are screwed.
If you are staying for a long time in any one country and you think you will need to use your phone buy a sim card in each country you are in - roaming fees from your home country are likely to be extortionate, because the phone calls and texts etc need to be relayed back to your home country and you will likely be charged loco amounts for making and
receiving calls/texts/etc.
Always carry some spare change, you will often have to pay to use public toilets - often about 50 cents.
Eurolines is a cheap bus company to go from country to country - 20 hour bus trips aren't pleasant, but they are often cheap. If you take a night bus, you are saving a night spent on accommodation. Just make sure you know which bus station you are arriving in at your destination, and have accommodation already lined up. There's probably nothing worse than arriving in a foreign city whilst sleep deprived, hungry, not knowing where you are, and having to find somewhere to stay.
Go to a festival - psytrance or any sort of hippy festival is always a good time with great people. I just spent 6 days at the Freedom Festival in Portugal and I honestly did not see one single dickhead (ok, there was one guy... but there's always one guy...).
One more thing - take the boat from Sweden to Estonia. It's very cheap and it's an enormous luxury cruise ship, complete with a supermarket, cabaret show and bars. The scenery off the boat just outside of Sweden is unbelievable and has to be seen to be believed. Estonia is very cheap, and Tallinn -although a bit of a tourist town- is very picturesque, very medieval and a lot of fun.
Speaking of medieval towns - try and go to Rothenburg ob der Tauber whilst in Germany - you can get there from Nuremburg (another really cool city) if you have a chance to go there whilst in Bavaria.
I could probably keep going with all this random information. but if you can think of anything specific you'd like to know, just ask or PM me - I'll help in anyway I can!
