Even though the title sounds quite general, this technique almost always helps you to a certain extent.
You know how you were/are told to drink 2 jugs of water a day, and your urine should be clear for you to take in enough water? I'm pretty sure almost all of us dismissed it and saw it only as a guideline, but the importance of drinking lots of water is monumental. A gigantic amount of the population who have access to fresh, clean water every day still suffer from water deficiency, but don't realize it because our body goes to big measures to hide the effects. Try drinking a lot more water, and carry a water bottle around with you regularly. I swear you'll feel much more revitalized and just better in general if you haven't been drinking enough water. Mind, I'm talking water, not kool-aid or whatever, so try it out today, and I'm pretty much certain it'll be helpful.