First of all, you should realise the price of tickets
. How important is the price for you? Most people say that it is the most important think. However, you should always remember that the lowest price could be connected with uncomfort travelling. Low cost airlines offers very low fares - but as always there is a catch - you have only small baggage allowance and almost no services.
Baggage allowance is the second important thing. If you are travelling alone and for a few days only it is clear that you don't need so many things. Holiday with your family is totally different example. You should always remember that you can carry only limited weight. It is worth to visit carries' websites and have a look at their baggage allowances.
Comfort. The question of comfort is not very complicated - you should decide in advance. If you are good with no refreshments and only basic service you can fly with low cost airlines. However, if you want to get free meal and have more leg room and better inflight entertainment you should buy airline tickets with scheduled airline.
These three basic tips should help you when you decide which airline you should choose. Enjoy your flight!