The Bruce Lee one is spot on - of course you need to think about something to get it done - but jumping in with both feet and not looking back I find is the best way to approach things....
I am a big believer in writing down key words to motivate yourself - I will do this nearly on a daily basis - words such as -
Drive
Motivation
Confidence
Power
Passion
focus
As stupid as it sounds taking a moment to reflect/focus yourself for the day and writing down the words you want to focus on or words you would like people describing you as is a really positive thing....