I have found that when I schedule exercise for myself, and not allow myself to think it over I have no problem getting out the door and going to the gym or going for a walk. If I think to long... I think about how hard it will be and the 100 things waiting on my to do list and I don't do it!
Schedule your exercise time - the same time of day is ideal whether first thing in the morning or right after work etc..A time when you're less likely to 'think' yourself out of it! Also schedule something you enjoy, right after... like your morning cup of coffee.. Gets you motivated to get it done!