This is a great book I discovered this winter: The Killing Zone.
It sheds light on the most common mistakes by low-hour private pilots between 50-350 hours, and it has statistics on which skills degrade fastest. (This can vary by country, but the items on the list are pretty relevant everywhere). So at least I can focus on practicing those, and this is why I bothered to fly from busier airfield in December, instead of our own, which is very quite these days. I also plan and mentally practice new flying routes for the springtime already, it helps me keeping my navigational / RT skills up.
The bottom line is: if you don't use it (at all), then you will surely lose it. Got to keep flying, got to keep practicing on purpuse.