Cost matters: Minimise cost and don't ignore taxes. Lower the cost, higher is your investment return and to hold onto your return, manage your tax efficiently. You can't control the markets (i.e return), but you can control the cost and taxes.
Discipline: Maintain long term perspective and stick to your plan. Market tend to be volatile in the short term and some investors may find themselves making impulsive or irrational decisions by not sticking to the investment strategy. Discipline, temperament and long term perspective are the qualities that can help investors to 'STAY THE COURSE".