Buy a "real" city guide
Most of the times the guide you have is just a small resume of what you can see in the city. A traditional guide will help a lot in planning the trip and making priorities.
Use public laundries
Do not wash clothes in hotels or even hostels! You'll find public laundries very easily. Almost every European city has at least one.
Go beyond the city center
When possible, visit more than the iconic and well known places that appear in your guide or you see in Internet reviews. Get out of the comfort zone, take a stroll and probably you'll find an interesting place with lower prices practiced than in the city center.
Save money with museums
If you love history, art and other values of Europe you have to know that there are many famous museums open to the public! It is a good time to visit what you like, enrich your knowledge without spending anything!
Don't be afraid to negotiate prices
Negotiate! In small hotels, small trips around town you can negotiate with the seller and easily get a discount of at least 20%. Pay in cash and negotiate!
Visit countries where your money is worth more
Visit countries with lower cost of living compared to other cities! Your choice on the destination of the travel can help save a lot. Go to countries like Greece, Spain, Portugal and Turkey. You will save and consume much more!
Pay attention to the calendar
If you want to save money, plan your trip avoiding big events.
Use wisely technology to communicate
Use the phone wisely. Avoid international tariffs because they are very expensive. Buy a prepaid chip, use skype, whatsapp and other applications to communicate. Easily you will find a place with free wi-fi like coffees and some hotels ... Do not use the hotel phone or make calls using the credit card!
Find the cheapest meal options
I recommend not to buy food in the hotel you are staying, it is usually very expensive. Do your shopping from a local store... Use specialized sites and applications to choose where to make your meals. You will find amazing restaurants, with very competitive prices. Many restaurants have a daily menu with starter, main course and drink or dessert for prices that will please you. Do not take breakfast at the hotel!
Save money with metro
Avoid the taxi! In almost all European countries the metro takes you to the main places of tourist interest, safely and quickly. Google Maps can help you choose the best alternative to transport. With daily or weekly bus pass (some exclusive to tourists) you will save a lot!
Travel in the low season
Comparing to the high season, in the low season you have many more offers in hotels and airlines. You will also face less queues at the main tourist attractions, saving time.
Use the discount sites
Some sites offer great discounts for hotels and flights. Try to book your flight one month before during the low season and three months during the high season. With this you can also save on accomodation because many sites offer great discounts to the last minute. Just find and take the advantage of promotions!
Moderate your shopping
Think before you buy something, you may buy something that will make you regret later because you could get it cheaper in another store.
Abuse the free attractions in Europe
Practically most cities will have free things to do. And even when they are not free, they will always have little discount. Museums often are free or have special days with discounts, look for this information. Many cities have free walking tours or an bus pass that let you combine several attractions.
Plan what you will do beforehand
If you are one of those who can not see what you will do in six months you risk pay more for a trip that could cost less.