Concentration is a key to better performance, and learning how to take control over your concentration will speed your development as a golfer.
A useful metaphor is that your mind is a camera, which registers images the lens focuses upon. You must train yourself to adjust the lens to bring into awareness what is really worth focusing upon.
The camera (mind) has a wide-angle lens and a narrow-angle lens. At times, the lens needs to be adjusted so we capture information from a broad area, like when studying a dogleg fairway from the tee.
At other times, we need to focus narrowly or zoom in on a discrete target, like when reading a putt.
Concentration exercises have been around for generations. Here are three simple exercises:

Visual Task

Attending to visual tasks causes neuronal firings in the visual cortex region of the brain, which may help you tune out distractions and focus. Daniel T. Moore, Ph.D., recommends improving your concentration and focus with a visual exercise using two different coloured pencils. Set a timer that goes off at multiple random time intervals for five minutes. For example, the alarm may sound after five seconds, then again after another 15, 10 and five. Hold one pencil in each hand, 16 inches from your face and shoulder-width apart. Exclusively focus on one pencil, then switch to the other each time the alarm sounds.

Chewing Gum

Chewing gum can improve your concentration by exercising attentional regions of your brain. This exercise involves chewing gum during learning or work-oriented tasks such as attending a lecture or doing homework. Chewing gum may improve your ability to learn, retain and retrieve information. Students that chewed gum during math activities for 14 weeks achieved higher test scores and higher final grades than non-chewers, according to 2009 data from the Baylor College of Medicine. Gum chewers scored 24 and 36 percent higher than non-chewers on immediate word recall tests and delayed word recall tests, respectively, during a University of Northumbria study in 2002.

Belly Breathing

Inefficient breathing patterns may suppress your concentration by limiting oxygen in your brain. Belly breathing exercises may improve your concentration and focus by correcting your breathing, which may improve learning and even boost your IQ. Place one hand on your stomach. Inhale slowly through your nose, and into your abdomen to make your stomach expand for about three seconds. Exhale for another three seconds by slowly pushing your breath out with your abdominal muscles.

Try them out and let me know how you get on.

From a golfers point of view the off (I should say) pre-season period is the most important time of the year.
The Old Mistake
A lot of golfers make the mistake of putting their clubs away for the winter thinking that they will not play as the nights are dark and the weather is poor. Then in March or April the clubs come out again and those golfers tend to play poorly for the first 4-5 months of the season. They moan about it and even try to cram some lessons in to get their game in shape as quickly as possible. The problem here is that these golfers are wasting playing time, they are not enjoying most of the summer golf season. The lessons are working but slowly as the golfer plays each weekend and reverts back to the old swing motion instead of sticking with the new improved one. In all it ends up being another year of frustration.
Do Something Different This Year
If a golfer wants to play well in the summer that golfer needs to do some preseason work in the autumn/winter. The months of November, December, January, February and March are the optimum time to improve how you play the game of golf. Imagine a football preseason. The team is at the stage of improving how they play: fitness, tactics, technique and practice games where the result is immaterial. The team is trying to be at peak performance for the start of the season. There is no difference with golf. When the weather is poor and performance on the course matters less because of team competitions or the fact that handicaps cannot be altered the pressure of scoring is off and therefore changes are made to technique much more easily.
Plan
An example of a really simple plan for the winter would be to:
1. Identify what you are wanting to achieve during the following season.
2. Go through your whole game and rate yourself out of 10 for each part of it. This identifies your strengths and weaknesses.
3. Look at the months of the year and plot how you are going to improve. A good example is this:
November- Mid January - Swing technique. Improve the golf swing to hit the ball straighter, longer, more consistently.
Mid January - Mid February - Swing technique but with all clubs. Begin to work on the worst areas of the short game.
Mid February - Mid March - Maintenance of swing, less technique. Routine. Heavy Short game work. Playing lesson.
Mid March - End September - Maintenance of swing and short game and 'emergency' sessions if needed. Mid season playing lesson.
October - Plan for following year. Enjoy your golf.
4. Practice and execute!!

If you have trouble or are not sure how to plan your improvement get yourself a lesson or two and I can help you understand how it can work. If you commit to it you will play better next year its as simple as that!