Proper personal hygiene.
Sorry to be Captain Obvious here, but really, I learned the hard way that you can't expect to smell like a petunia if you don't walk your butt through the shower every now and then. If you've got some bad body odor, you should shower or bathe at least twice a day and use a good antibacterial soap. It's also important to only use your rags and towels once. After you rub them all over your body, they become filled with skin cells, oils, sweat, and other nasties that those bacteria we talked about earlier love to eat. Probably not a good idea to rub that on your body again.
Things not to eat.
Because your body exudes toxins through your skin, the things you eat can make you stink. One of the worst things you can eat, as far as body odor is concerned, is red meat. And for obvious reasons, you should try to avoid things like garlic and onions. I hate to say it, but coffee is bad, too. Actually, any caffeinated beverage is bad in the smell department. Caffeine can cause excessive sweating. Other things to avoid are fatty foods, fried foods, refined sugars, and overly processed foods. If you have a fishy smelling body odor, there's a good chance your body has a hard time processing choline. Choline is a nutrient found in fish, eggs, liver, and beans. Finally, if you suffer from bad body odor, you really should avoid alcohol and tobacco, too.
Things to eat.
I know it won't be easy to give up eating and drinking the things I mentioned above. You will just need to decide for yourself what's more important to you: indulging in things that give you body odor or not smelling like a foot. In the meantime, there are still plenty of good foods available that do not contribute to body odor. Almost all fruits and vegetables fall into that category, especially foods that are high in chlorophyll (a natural purifier and odor eliminator) like parsley, spinach, kale, and other leafy greens. Breads and nuts are good, too. Like I said before, eat foods that aren't highly processed. Go into any natural foods store and start shopping. Just skip the red meat section.
Have yourself a good sweat.
Yes. I am fully aware of how counterproductive this idea seems. But think about. If your body is exuding smelly toxins that make you stink, wouldn't it make sense to hurry up and get rid of them? By causing yourself to sweat, you clear your pores of those toxins more quickly. There's a number of ways to do this. Exercise, of course, is the most obvious. However, sweating can also be achieved by sitting in a sauna or a hot tub for awhile. Whatever you do, shower afterwards and wash the stink off. Before you attempt to sweat the stink out of yourself, make sure you're properly hydrated. Not only will this keep you from dying a terrible death, drinking lots of water helps to flush your system.
Further underarm odor control.
Relax. The commercials are right. Stress stinks. Find things to occupy your mind with other than your money/work/relationship/family problems. Go for a walk, play a game, listen to music, etc. Whatever you decide to do, do it in clothes that breathe, such as cotton or silk, and make sure they're clean. Never re-wear clothes without washing them. Don't sleep in a dirty bed either. Change and wash your bedding at least once a week. After the laundry is done, start shaving. Men and women, shave your pits and your genitals. Hairs provide a lot of surface area for bacteria to grow on. Excessive armpit hair also makes it more difficult for you to actually hit your skin with deodorant. Men, I'm proud to say that I have shaven pits and a shorn scrotum. It takes fifteen minutes about every three weeks with a beard trimmer. One final thing: carry some moist towelettes with you. Sometimes you're gonna get stressed and there will be perspiration. Be prepared to keep yourself from stinking.