Anyone can say “I want to get fit,” or “I need to lose weight.” But what's your personal finish line look like? Is a weight on a scale? Inches on a waistband? Number of pull-ups you can successfully execute? To have the proper motivation you need to have a goal—something to work towards and certainly something by which you can measure your progress against. Be specific and track your progress. When you see how far you've come, it's easier to get back on track if life gets in the way and you have a few too many margaritas (and too few workouts) on vacation or indulge at someone's birthday dinner.

So many gym-goers fall prey to this. You show up, look around to see what you want to do, and start working on a few machines or hop on a treadmill. When you don't have a set plan of attack, your workouts will no doubt be shorter and less effective. So you need to start by developing a plan and then have the patience, fortitude and commitment to stick to it. “A program should be developed around a person's age, goals, diet and time,” says Steve Kamb of Nerd Fitness, who offers everything you need to factor in to start your own plan on his site. “Developing a workout routine for yourself can be scary, but it's really not too difficult and kind of fun once you understand the basics.”

A human body reflexively backs off when it gets uncomfortable, as you've no doubt experienced. Many guys may put in the time at the gym but not necessarily the effort required to get the results they're striving for. Ask a personal trainer how often they have to ask clients to slow down or ease up and they might just laugh. Once you've set your goals, push yourself to achieve them, try to beat your personal bests and results are all but guaranteed.

It's understandable that a guy would want to lift as much weight as he can. But that effort doesn't do much for you, especially if you get hurt, says Tom Holland, exercise physiologist and author of The 12-Week Triathlete. Instead of straining under all that weight, Holland suggests focusing on the quality of the movement instead, using slow and steady movements to see the most gains.

You can spend all the time in the gym you want, but if you're not eating clean, you won't see what you want in the mirror. If you want to lose the spare tire, the most important exercise you should be focusing on is what you put in your mouth. Diet will have the biggest impact on how your abs will look. The easiest solution? Lay off the sugar and refined carbohydrates. And it's not just food—alcohol is one of the easiest ways to sabotage your progress. Especially because booze leads to excess calories and often a loss of motivation thanks to that stubborn, angry beast known as a hangover. Your best bet is to limit your drinking to one night a week. And when you do drink, aim to go one-for-one with water and alcohol to help you stay hydrated and stave off hangovers.

Even those who understand you can't spot reduce fat often spend way too much of their time in the gym doing crunches in order to get a six pack. Or only perform dumbbell curls to build up their arms. But compound moves like squats, push-ups and pull-ups are key. They work the body as a unit, burning more calories in the process. Your body needs variety. If your muscles aren't challenged, they won't get stronger.

You'll never be able to give your all or even put up a good fight when you have a sore back, painful knees or a shoulder that screams with most movements. When the pain is dull and general or sharp and isolated to a specific area, you want to treat it and give it rest (and maybe even see a doctor) before you get back to regular exercise. If you don't, you run the risk of permanent damage or a larger, longer setback. More importantly, you want to avoid movements that cause or lead to injuries and pain before they happen.