Thanks for writing. One of the biggest dangers of using potting mix from season to season is that disease organisms can overwinter in the soil. So if you had disease issues last year on any of your container plants, I'd toss that potting mix in the compost heap and start over.
If your plants were healthy last season then you should be able to reuse the potting mix. Remove it from the pots and pour it into a large bucket or container. Break it up so it becomes loose and fluffy, then saturate with water and use it to refill your container.
You may want to fertilize your container plants during the growing season, depending on the type of plants you have and how much you want them to grow/bloom/produce fruit.
---Justin, Senior Garden Editor, BHG.com