The most common mistake that people make when buying a midlayer jacket is to get something that is the wrong size. Whether too large or too small, keep in mind that this jacket will be work as a layer and therefore must be able to accommodate other clothing above and below it. Think about how you like to layer so that you can purchase something that fits perfectly. If you are going to deviate from your normal size, sizing up is usually the better choice.
The other common mistake is to buy a jacket that is to warm and lacks breathability. Thinking about your jacket abstractly you may believe that you need as much warmth as possible. Warmth is important of course, but this jacket is meant for active use, making breathability more integral for comfort.