Taking stock in this way is a little like a performance review - though I hope a little less stress-inducing than those at the office might be. It's an honest accounting of the good, the bad, and everything in between, and it's not always simple. It may take some time, because you need to identify the "why" as well as the "what."
First, make some lists
In a book or a journal, start making lists for the good and the not so good of the last year. For example, my good list includes some of the dinners we had on the beach over the summer and my bad list includes our disastrous Halloween. Our summer vacation is on both lists, actually, because there was both good and bad in it.
Your lists can include both concrete events and general feelings. If the late winter was particularly good time, just in general, note that.
Second, make sub-lists
Okay, now take everything on those list and make some sub-lists for them. Try to identify why they were good or not so good events.
For that lovely late winter, what specifically happened - or didn't happen - that made it fun? Was it the weather, or lack thereof? Was it specific activities or non-activities? For the not-so-good events, identify the same kinds of issues.
Our vacation, for example, was great in terms of family togetherness and new adventures but not so great because we tried to do too, too much and a couple of very rainy nights in the tents.
Third, identify that over which you have control
All those sub-lists include things over which you have control or partial control - and things over which you have no control. Be honest here - and this is where it might get a little hard - there are some things that you claim to have no control over that maybe you do, just a little.
For example, a specific kid meltdown might seem like something over which you had no control...but did you expect too much and did that expectation set up a chain reaction of events resulting in the meltdown? I'd mark that as a partial control situation. You may not be wholly responsible, but you had a hand in the situation.
For things over which you had control, learn from those items right away, whether the source events are on the good list or not-so-good list. If those evenings out were the result of good planning on your part, that's definitely something you want to repeat.
For things over which you truly had no control, especially on the not so good side off the list, try to learn one thing from the situation if you can - then just let it go. You can't control the weather, for example, even if you can remember to check the forecast more frequently and prepare accordingly (or have a contingency plan).
Finally, cut yourself some slack
For all the good and bad and in between that happens in a year, remember that we are all human, and we are all doing the best we can. Sometimes things go great precisely because of our best efforts, and sometimes they go screwy in spite of our best efforts. It's impossible to be perfect, and it's more than okay not to be perfect. Taking time to take stock just helps us move forward in the most productive ways.