for me i look way ahead and try to book about 11 months in advance, it works for me, i use skyscanner first and once i have a price to work on try the airline and mix a few dates in that can save you hundreds of pounds by just going early or a later date, also think of a price and if you are happy with it book it, dont be fooled by a cheap price on line, once they have added tax and anything else they can you may be better of going with another airline, also watch out for times you may be waiting for the next flight, try to get the shortest time at the airport and that includes both ways, good luck