An often overlooked key to success is mental training – just like any other skill we develop in life, our mental competence is a muscle that must be exercised. Below are 11 key areas to focus on, divided into 3 main categories:

Seek to learn new things everyday

educate yourself (through school, podcasts, reading books etc.)
expand your vocabulary (if you hear or see a word you don't know – look it up)
work on a side skill every week (painting, writing, sports, cooking, woodwork, learn another language, whatever interests you)

Exercise mental discipline

lessen your procrastination (do the hard stuff first)
maintain a productive routine (wake up at the same time, x amount of work per day, x amount of exercise per day, etc.)
challenge your skills (up the difficulty each time you feel comfortable)
challenge your beliefs (entertain all ideas – you don't have to buy into them, but hear what people have to say)

Work on your emotional intelligence

feed your brain (stabilizing your emotions starts with adequate nutrition (ahem omega 3s) – you have to feed your brain for it to serve you powerfully)
forgive yourself (there is no benefit in holding on to past regrets. From now on you must look at yourself as a clean slate.)
get rid of those holding you back (negativity, shady friends, judgemental peers – their emotions will rub off on you if you keep them around)
learn how to apologize and take criticism gracefully (easier said than done, but learning how to do so will go miles in developing positive relationships)