The idea of mental training is essentially the same as that of physical training. You engage in certain activities to build the skills and "muscles" of your mind. The following examples are based on the latest research and personal experience.
The Brain
Science has shown conclusively that we continue to have the ability to grow new brain cells as adults. The specific activities that seem to work best for this are both mental and physical. The physical activities that work best include those that involve hand-eye coordination, such as playing tennis, climbing, and even woodworking.
The more mental activities that get the brain in shape are those that involve concentration and new experiences. Learning a language is a great example. Crossword puzzles and similar mentally-challenging games are useful as well. Puzzles and even some video games can help (the latter often require hand-eye coordination as well).
The Mind
Keeping the brain "tuned up" is a good start to mental training. In addition to the activities mentioned, proper nutrition can help with that too. But for the most mental power and abilities it pays to turn your attention to training of the thought processes themselves. This is where the most dramatic gains can be made.
For example, you can start with something as simple as learning to ask several times daily, "What other way is there to see this?" If you are dealing with a problem at work, this question might get you to see the perspective of the other people involved, and that can lead to a new resolution. If you are watching the evening news, you might ask the question of a current political issue, and so realize that the commonly argued positions are not the only ones available.
Powerful questions of all sorts are great for mental training. The question, "What other uses could this have?" could lead to a hundred new innovations of asked often enough. "What can I do about this?" is a question that gets us past disabling blame or apathy.
The key is to develop a habit of asking these questions. One way to do this is to write a few of them down on an index card and carry it with you at all times, preferably in a pocket that you reach into often. In general you need to consciously do something for a few weeks for it to become an unconscious habit. Once you have made it habitual, you will find that the change is often permanent. This is because the rewards from good habits reinforce them. In this case, you'll be rewarded with new and useful ideas.
We all have many habits-of-mind already, and we know how persistent they can be. Some people routinely complain, for example, or always find the flaw in anything suggested by others. We can see the negative effects habits like these have. Complainers enjoy life less, and critics not only chase away the people around them, but also dismiss their own ideas, even when those ideas may have been developed into something useful. But even knowing this, most people have a hard time changing. This is sad, perhaps, but it also suggests something very good: the power of habit.
We can use that mind power. If you consciously asked "What is good in this situation?" or "What can I do with what I have here?" - and you did this until the questions automatically arose from your unconscious mind at every opportunity, how much more effective could you be in life? That is the power of good mental training.
