I like Russell’s way of doing it. I also like to do it first thing in the morning. Aside from the fact that I feel a lot better throughout the day in starting with a workout or run, it just takes care of it before I have a day to get tired and fret over whether I should do it or not - it’s already been done.
A couple of tricks that help me get up early and out the door are to keep my alarm clock across the room, so I have to get up to turn it off. It can also be helpful to have your shoes, clothes, etc. all ready and easily accessible so you don’t have to put any effort into being ready to be out the door. Maybe you can also make a habit of creating a playlist on an mp3 or cd player that is for Mondays which has favorite music that you save for only this day, thus making a special, enjoyable occasion of it - “hey, today is monday, but at least I have good music!” Another thought is to find a workout partner who would join you on Monday to build in some accountability (good ol’ peer pressure), or find yourself a good class to attend and make some friends so you have more reason to feel like going out on Monday.
I’ve found that simply doing it for a period of time - maybe a matter of weeks - forges the habit and it becomes not only easy, but a comfortable routine. Perhaps with using little tricks to make it easier to do and sticking with it for a little while will help Monday workouts to become a natural, enjoyable event for you