There is no conclusive evidence that people preferentially use the left or right hemisphere. 
Certain functions are processed more by one region of the brain than others, and this is known as lateralization. But we all use our entire brain equally.

Right or left-brained

Both of these study strategies are relatively ineffective. Passively reading the same text over and over again won’t do much for recall unless it’s spaced out over time.

Re-reading and highlighting

One study found that 75 % of college students and 55 % of instructors believe that <a href="http://psycnet.apa.org/doiLanding?doi=10.1037%2F0022-3514.88.5.725">changing their initial answer</a> would lower their score overall.
A review of 33 studies found that, on average, people who change their answers score higher on tests than those who don’t.

Sticking with your first answer

The theory stating that we only use 10 % of our brain is an urban legend. It seems to have originated from the 1930s self-help book “How to win friends and influence people,” (Dale Carnegie) in which a Harvard University professor was misquoted.

10 % of our brain

The theory says that people remember 10 % of what they read, 20 % of what they hear, 30 % of what they see, 50 % of what they see and hear, 70 % of what they say and write, and 90 % of what they do or teach others.
This is never actually been proven and the percentages given are pure fiction.

The learning pyramid

Despite all the learning fads that have come and gone, from mindfulness to brain training games and exercises, learning is and will always be a process. It requires time and effort and is bound to feel difficult and uncomfortable at times.

Shortcuts to better learning

A growing body of research shows that our IQ can increase over time, and in fact, research on growth mindset by Stanford psychologist Carol Dweck shows that our beliefs about intelligence can actually affect our effort, and in turn, our performance.

Intelligence as a fixed trait

Systematic studies of learning styles have consistently found no evidence or very weak evidence to support the idea that matching the material to a student’s learning style is more effective.
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Different learning styles

There’s no magic number of hours that will turn you into an expert .A Princeton study found that deliberate practice can only predict success in fields with stable structures where the rules never change, such as tennis, chess, or classical music. In less stable fields, mastery requires more than just practice.

The 10,000-hour rule

Research on the growth mindset by Carol Dweck found that praise can actually be counterproductive and discourage people from taking risks.
Dweck’s research shows that praising effort and persistence is a much better way to motivate people.

Praising intelligence

Science is constantly changing, and although we've come a long way since the days when it was widely believed that older people couldn't learn new things, a number of learning myths have stood the test of time despite having no grounding in scientific research. Tom Bennett-teacher, author, and director of ResearchED-points out that there are...

10 % of our brain

Similar ideas to 10 % of our brain

Myopic points of view

The blurry line between psychology and self-help