I got this from my current instructor, so maybe it will help you as well.

#1 Work in 90 minute intervals, and then take a break. Overworking can lead to stress and can exhast you. Even if you just stand up and stretch or get a glass of water or breathe deeply for 5 minutes it is better than pushing yourself too hard.

#2 Take time to relax, sit up straight in your chair, breathe in through your mouth and out through your nose. Take Diaphram breaths, deep breathing like an Opera Singer might take. Imagine you are at the best vacation you ever have been to or wanted to go to. Think positive things and relax. Then start working.

#3 Drink plenty of water, as being dehydrated can make things worse. For one it can lead to more stress, for another it can cause your body to not burn off enough fat. If your lips are chapped or dry and your hands are dry, drink more water. Doesn't have to be bottled or from a machine, tap water will do as well. Your brain also works better with the right amount of water in your body.

#4 Get plenty of rest at home before going to work. If your body is exhasted, your mind and spirit and emotions will follow.

#5 Learn to pace yourself. Don't always hit Home Runs, try to hit Singles too. Singles do add up and complement Home Runs. Can't get a Grand Slam without three singles.

Best advice a co-worker gave me is to imagine you are eating an elephant. You cannot eat it all in one day, and you have to take small bites, until eventually the elephant is all gone. Or to cite "What about Bob?" take "Baby Steps".