In Leo’s post The Ultimate How to Get Lean Guide, one of the fitness experts says to try adding caffeine 30 min. before a workout to boost intensity. Another recommends a few cups of high-quality green tea a day.
I unwittingly combined these just awhile ago. I noticed I would sometimes feel groggy when I was going to go workout, and after 10 or 15 min. working out I would want to stop (my workouts are usually pretty intense, lasting no more than about 30 min.). I started drinking some green tea (usually half a cup to a cup) before heading to the gym (caffeine takes about 30 min. to kick in, so it would typically start to kick in part way through a workout).
It worked (and also associates the feel-good that comes with caffeine to going to the gym, which can make it more easy to get going to the gym*).
Also see How to enjoy going to the gym.
Have fun!
*Caffeine, like pretty much anything, if over-used can cause various problems, including stress and sleep problems. Using only green tea reduces the chances of this, as the amount of caffeine is relatively low. I have about 2-3 cups of green tea a day right now.