How long is a piece of string? This is a hard question to answer however there are a few basic rules to follow. Flights can be booked about 10 months in advance depending on the airline. Normally the cheapest months to fly is out of holiday season as the fares are more expensive during school holidays, Christmas and Easter. They also increase when there are major sporting events around the world and the school holidays also overseas count as well.
Weather also plays a big part in the prices; cheap airfares are available to Asia during the monsoon season but although the fare may be cheap you will also get very wet. Early bird fares are normally released around September however each airline will only release so many seats per fare so the sooner you get in and book and pay the better the fare.
No longer are the days when fares would get cheaper the closer to the departure date just to fill the planes.... the good old standby fares no longer exist as planes are very heavily booked. Hotels and resorts plan months and years in advance and know when their low seasons will be and offer packages and discounts way in advance to fill these. Again, school holidays are peak time for not only flights, but hotels, car hire and tours.
Cheapest times to fly are normally outside the peak time e.g. early morning and afternoon from 3.00pm onwards is when business travelers would fly hence they are peak times. Fridays through to Mondays are expensive as again people book to go away for weekends. Midweek and during the day from about 10.00 till 2.00pm would be the best time to try and snag a good price airfare.
Cruises - I recommend you book way in advance and this can help you get a great price, the cruise you want and normally the cabin you want as well. A lot of cruises are booked out 2 years in advance so you need to get in early. October is always a great month to have a look at the cruises as this is well known as being ‘Cruise Month’. The great thing about cruising is that you can book it and pay the deposit and then you can change it, cancel it up to about 6 months before so let your Travel Counsellor look after this as we can do things you can't.
So, the question was when is the best time to book travel and the answer I would give is as soon as possible.