Most people get freckles in the summer, when they are most exposed to the sun. Actually, this is really the only way to get freckles, and even then you may not get the results you want, as most people are born with them. Even so, getting some sun can be beneficial.
Make sure to wear sunscreen, and don't damage your skin by getting burned. Just take care of your skin in general: moisturize daily, and exfoliate! Hope this helps :)