The following things can be best done to save on your trip to Europe:
Do not book round trips, book one-way trips
Try travelling during the off season
Before buying anything anywhere, always compare prices
Don't spend on expensive mobile data plans, because free Wi-fi
Book family rooms rather than multiple rooms
Save money by travelling through rail in Europe
Choose to eat food that is seasonal
Try to walk everywhere. This will save you money, and help you explore cities better