Motivation is something found within one’s self. For weight loss I let them know they are doing a great job, and then we look at their stats. First is their diet, a lot of times little things start to creep in, like taste testing, an extra snack. Make sure that they are at the low end of their calories allowed per day. The next step is their cardio: are they mixing it up? If they are always running, I will switch them to cycling, or ellipical machine, or one of the many group classes offered at the gym. Not only will this increase their calorie burn, but more important it will get them into something new and hopefully get that motivation burning within them. Strength training, mix it up, increase or decrease the weight, do more circuits, or more set training. Bring something fun in, like a hula hoop, can’t tell you the smiles I have gotten from somehting that simple.
Another thing I have used is coupling up two clients with the same goals. Train them together every so often, they build a relationship and work together. They realize they are not alone.
These are a few things that have worked for me. Good luck.