Usually at the end of December I take time to look back on the year passed and do some category assigning. These categories range from "don't want or need to go through that again" through to "yes, more of that please!" Life sure can seem like a roller coaster sometimes, right?!
Anyway, for anything that wasn't so pleasant - there may have been a lesson in it somewhere, even if it's a simple warning on how to avoid anything similar in the future. After extracting the lesson, the experience can then be let go - as it is no good to keep hold of it anymore. Also it's not good to suppress, because it will just come back up again later. There's a difference between letting go and suppressing. Think of it like a beach ball and water - if you force it under the water, it will resurface when you relax your hold. Where as if you just let it go and pay no attention to it, it will just drift away.
As for the good stuff - well done! Celebrate the successes. Look for ways you can repeat or even improve on the great experiences if that is what will be beneficial to your future plans.
During reflection time it can be easy to slip into comparison mode. But do NOT compare to anyone other than yourself! You don't know the other person's journey, and you don't know their entire big picture - they may succeed in one area, but fail miserably in another area. We are all unique and have differing sets of values and priorities. Here's a good quote (unknown author) “Everything in life is easier when you don’t concern yourself with what everybody else is doing.”
Have kindness and compassion for yourself as you reflect. Think about what you'd like to take with you into 2019 and what you can happily say goodbye to.