1. Play the hemispheres. Northern hemisphere's winter is the Southern hemisphere's summer and vice versa. Escape the cold by traveling to the opposite end of the world!
2. However, remember that depending on what your interests are, hotter is not always better. For instance, Buenos Aires is a notoriously stunning city, but you may enjoy it most when it is at the beginning of the season when the weather is temperate versus being in the city when it reaches the high 90s. This is true for most city vacations.
3. Always be sure to research the weather of your destination. Look at the 10 day forecast surrounding the dates of your trip, and even pull up the weather records for those dates in the years prior.
4. When you're traveling "off season" so that you can take advantage of lower rates, remember that the particular season is "off" for a reason, and it's usually because that time of year enjoys the worst weather conditions. So, bare this in mind and structure you activities accordingly.
5. Structure your days and excursions so that they are not all weather dependent, and have alternative activities in mind. Too many people travel to a destination famed for its sunshine and then don't know what to do when the weather doesn't cooperate.