Just ask your fellow passengers what they paid for their flight. You'll hear a lot of different prices, if not all different. Hopefully you ticket is the cheapest ....
The answer is; by trying out the same trip in as many online booking engines and choosing different travel dates. Repeat this a few days in a row. Besides many different fares for the same flight you'll be faced with unexpected surprises. For example, a plane that one day only expensive business class seats available the next day yet again have economy class seats. Apparently canceled one or more passengers. Looking after midnight and the morning before day and dew. New offers are usually in the night hours posted in the internet booking systems. With a few days of solid surf-work impossible times, you can save yourself hundreds of euros.
If you want ticket consists of two or more sections and you have to change in a fun city, you can determine whether you can make a Stop over 'of a few days. Almost every ticket entitles there! In the online reservation systems, this is often not settle, but there is something going on. See if you come across IM services and phone numbers on the site. Employees of the tour stop on it for you to capture. Single tickets can also buy, but it is generally more expensive.
Do not think you've found all flights if you've plowed through the online booking engines 10 major tour operators on the desired route. Not all airlines are affiliated with these systems. Price Fighters like RyanAir and companies only nationally or regionally fly you not think. These can however be very interesting. If you're on a composite ticket and must change can happen that companies not included in the international reservation systems occur have a better solution for part of your trip. By clicking on some routes to make use of the routes of low-cost and small companies, open up new routes which may be more advantageous in total are in that way. Finding those routes and airlines is work for the real "air-cowboys. They make their journey together from tickets 'ordinary' airlines, budget airlines and regional carriers. Long live the Internet, you'll find them all. Who wants to know more about this subject can read my article How to find all cheap flights.
Many travel fun!