Decide. 

Nothing builds momentum like decisive action. Similarly, nothing kills momentum like confusion and a lack of clarity. Just decide. 

Decide you’ll be done with it today. 
Decide you’ll set a new bar. 
Decide it’s time for a change. 
Decide this will not stretch out past the week. 
Decide this month is the month you make it happen. 

In the words of Randy Pausch, decide if you’re Tigger or Eeyore. 

Decisive action is motivating, it builds momentum, and it crowds out excuses. There’s no room for excuses when you’ve made up your mind and that’s exciting.