Ok, so after reading every page on the site, you still have some questions. Well, you've come to the right page, here we'll try and answer your questions as simply as possible...
The general rule of thumb is the sooner the better, especially if you want to work in a particular resort.
For jobs in Europe, most companies start their recruiting in May/June, with the aim to have all positions filled by October. That said, there is still the possibility of finding work once the ski season has started, as companies need to replace staff that have left before the end of the season.
If you're looking to work in North America and need a work permit, you will need to get your application in much earlier. This is due to the length of time it takes to process temporary work permits.