So often people think of exercise as a chore. I know I used to. January of 2009 I changed that mentality and joined a women's only dance studio. I danced my weight off. Later I incorporated riding my bike and roller blading. The main thing is if I don't love it I won't do it so find things you love.
After a lull in your motivation and you feel that burst of energy to get going on your goals again don't wait until Monday or tomorrow to start. Start right now!