Hi flybie, welcome to the Europe forum.

It's a difficult question to answer, as it's so wide open!

Specifically for tips on low-cost travel, we do have a Budget Travel forum, which has lots of discussion and resources you can search and browse for.

Specifically within Europe, general tips I'd give are:

• Check sites like airbnb.com and hostelworld.com - it varies according to region, but there's some real bargains if you want to rent a room in someone's house (or have a studio to yourself). Couchsurfing may also help you get free accommodation.
• Choose the countries that you visit carefully. Places like Portugal, the Czech Republic and Croatia are significantly cheaper than Scandinavia and the UK, for example.
• Look at rail and bus travel as well as flights - much of Europe is well served by rail. You'll only normally get cheap rates through the national or local operator (not a site like raileurope.com). The German railways site bahn.co.uk is good for getting timetables (and fares to/from/in Germany). If you're not too picky, you can sleep on overnight services for little money (if you are picky, you can pay a bit more for comfort...)
• Sites like dohop.com and skyscanner.net are good for comparing low-cost and full-service airlines side by side (but do factor in luggage fees etc!)