The winter is the best time to improve your skills and take a mountain bike skills camp. Many skills, such as cornering involve a lot of different movements/components which means practicing "cornering" is not deliberate practice. Deliberate practice would be practicing vision through a corner three times, stopping and analyzing what you did right and wrong then refocusing and doing it three more times. This is why you see all the basketball, football, ski teams and pretty much every sport requiring skill teams doing drills more than 70% of their practice time!
A few weeks of this quality practice (mixed with resistance training and cardio work) will do more than years of just winging it on the trail (according to Ross Schnell who said, "I learned more today than in the last 10-11 years of just riding" (in a rushed 3.5 hour lesson, BetterRide camps are 19-22 hours over 3 days!).