Kuki has it right in that the two best times to book are; as far out as possible and around 90 days out to a few weeks before the cruise.
The BIG DIFFERENCE is that cabin selection is limited the closer you are to the cruise.
If you want your choice of cabins then you want to book as far out as possible. Choice balcony cabins will sell out first. The last minute bargains are usually limited to inside and outside cabins. Once in awhile you may find some balcony cabins or suites but it is hit or miss.
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"There is a great difference between being well traveled and just having been to many places." ~Me