There are so many places to visit and see that is does seem really daunting, but I also recommend seeing less places better...I planned to go to a lot of places but saw less and do not feel hugely upset that I did not see all the places I wanted to, as I got a lot out of the ones I went to ( including several places not even on my radar before I left).
Maybe to get your feet,start off in some cities eg London ( which is where many people enter Europe from) and spend a few days getting to grips with being somewhere ( but english speaking) and how things work. Most cities work in the same way eg transport, tourist centres, tours etc.
I would chose a few major cities and work your way around them...try also going more east and I loved Prague and Croatia...they rate higher than places like Amsterdam, Belgium etc for me. THe other thing to consider is what you are going for, eg meeting people, partying, drinking and add in sightseeing or are you going for shopping or culture/history?
I went for the latter so thats what i based what and where for the most part. Going with hostels are a good way to meet people to wander around for a day or 2 ....try something like www.hostels.com, www.hostelworld.com, www.hostelbookers.com or www.lonelyplanet.com.
Also look for some variety in places eg near the sea, near mountains etc and things they offer eg type of history eg medieval, renaissance, roman etc.
As i pointed out, really cutting down on the number of places you go and seeing the places you do go better is in the long run FAR better, otherwise you will in stations/airports/bus/train/planes for more than you are seeing the place. I saw northern/central Italy in just under 2 weeks and that was not long enough for me, I did Paris in 5 days, Prague in 5 ( too many so I did 2 day tours to fill my time which were great especially to Cesky Krumulov), Rome 3 1/2 ( not enough) and Croatia/Slovenia in 2 weeks. Some places need only a night while others require more time. Also travelling all the time ( apart from being annoying) is very tiring and a few weeks of this gets tedious, so have some larger cities where you can base yourself and do some day tours or day trips ( depending on if you want a guided or a DIY) from there.
Do some research as well to get the most out of your time, get a vague plan covering some places you would like and put it to some people who have been and see what they comment on or recommend to do there, how long to stay and what you can do from there.