No.10 Down the fruit juice

If you’re looking for a quick way to put on weight, start downing glass after glass of fruit juice. While often thought to be a healthy beverage, it's really anything but. It contains far too many carbs to be on a fat-loss or weight-maintenance diet and what's worse is that a large portion of these carbs will be fructose, which gets converted to body fat much quicker since it can't be stored in the muscle cells. Solution? Opt for water, milk or green tea.

If you're the type to avoid drinking throughout the workweek and then go out for a night of partying on the weekend, you're going to get fat. It's quite easy to consume well over 1,000 calories on a good night of drinking, and if you add up all the chicken wings, pizza and peanuts you consume while you're at it, you could be looking at a full pound of fat gained over the course of the evening. As far as your waistline is concerned, limit alcohol consumption to one or two drinks a night, on occasion.

No.8 Eat carbs

If there's one thing that can make you fat quickly, carbohydrates would be it. High-carb foods, especially of the processed variety, are extremely dangerous in terms of fat gain, because they'll quickly cause your insulin levels to soar, which puts the body into a fat-storing state. With all these calories floating around in the blood with nowhere to go -- unless you've just done a very intense workout -- they're fated for fat storage. Always keep carbohydrate consumption to a moderate level and be sure to balance them out with a lean protein as well.

No.7 Eat out

Another thing you should avoid doing is eating out frequently at restaurants. Many people do a great job at avoiding fast-food fare, but what most don't realize is that dine-in restaurants are almost twice as bad. The average entree can easily pack in well over 1,000 calories and is often processed, so if you want to prevent fat gain, cook at home as often as possible.

No.6 Take the car

As much as you might focus on getting in the most intense workout sessions possible, failing to look at the everyday ways you can be active will really cost you. If you hit the gym regularly but then drive everywhere (and are all-around quite lazy), this will significantly lower your overall calorie burn for the day. Just by getting out of the car and walking around more often, you can easily burn off 200 to 500 calories per day. Easy, right?

No.5 Eat greasy food

If you are going to cheat on your diet, the worst foods to do so with is high-carb, greasy fare. When you consume foods that are both high in carbs and high in fat (such as pizza, doughnuts or burgers), you're really hitting the body hard with excess calories that will lead to weight gain. Now you'll have raised insulin levels from the high-carb intake, and with those insulin levels high and your body in prime fat-storing mode, you'll quickly take the fat up and store it. If you're going to cheat, do so with lower fat, higher carb foods. This way, with the raised insulin, all the excess carbs can go toward the muscle cells to refill muscle glycogen, thus reducing the chances that you gain body fat.

No.4 Use commercial weight gainers

If you're someone who's trying to pack on lean muscle mass, you might be considering the use of a weight-gain product. If you want to stay lean, however, you'll want to rethink this. While you may require a high-calorie intake to build muscle, some of these commercial weight gainers pack in well over 1,000 calories, which is too much for even the biggest weight lifter. Plus, these commercial weight gainers are often filled with simple sugars, which will wreak havoc on your body and set you up for diabetes. Instead, create your own weight gainer using protein powder, raw oats and flaxseeds.

No.3 Load up on the wrong proteins

You're aware you need protein to build muscle, and you take this information to heart. Day after day you're loading up on all the high-protein foods you can find and don't feel ashamed to indulge in a juicy 12 oz steak when the opportunity presents itself. If this describes you, you may very well be on your way to gaining body fat. Remember that many protein-rich foods do contain high amounts of saturated fat and calories, so consuming too many of them will put you on the quick road to obesity. Instead, choose leaner sources of protein, and consume them in moderation. Men naturally gravitate toward protein-rich foods whenever they have a craving, but remember that you can get too much of a good thing.

No.2 Move back home

In today's tight financial times, more and more adults are choosing to move back in with their parents. If you're looking to maintain a lean body, though, this may be the last thing that you want to do. Surrounding yourself with all of your mom's high-fat, high-calorie cooking will likely lead to excess calorie consumption. With someone else doing the cooking and you strictly focused on the eating, you're headed for a bad situation as far as your belly fat is concerned.

No.1 Forgo your muscle-building workouts

Do not not skip your muscle-building workouts. What some men fail to realize is just how much of a boost they will get in their metabolism and this could mean the difference between you staying lean at the end of the day and you gaining body fat by night's end. You can burn up to 200 calories over and above your usual expenditure after a very intense workout, so don't ever underestimate the power of muscle-building workouts.