|haha, thought this was appropriate :)|
Develop a routine that you have to adhere to! My routine consists of cardio every day, and then I rotate between arms/legs one day, and abs the next day. This motivates me to not skip the gym, because then my days would be all confused.. and for someone who plans their life out, that stresses me out :) It is also great to confuse your body by doing different exercises! Work as many muscle groups as possible and build that bod!
Like I mentioned before, tracking your workouts is one thing that totally motivated me to not skip days at the gym. Find a small notebook, tape a piece of paper to your wall, or create a "note" in your iPhone where you HAVE to log your workouts! On the days that I really dread the gym, I think about how I'll have a x-mark on my skipped workout day... and that alone motivates me to do my workout :)
Now, don't forget, you don't need to workout EVERY day! Give your body a break so your muscles can recover! It is all about scheduling!