I'm here to share my experience with you. While I have yet to meet my goals (still fat), I'm finally on the right track. When you do the little things right, everything else falls into place.
The single most important thing to remember is to start small. The majority of people think they can just jump into a healthy life-style, but they're wrong. That's not to say everybody fails, just the majority. The word of power is consistency. Small is much easier to maintain than large. You need to start small.
By this, I mean for the first week you need to pick one thing and change it into something a healthy person would do. I chose breakfast. As the most important meal of the day (though some would argue that), it is the foundation of your fitness. It has been said that nutrition is 90% of the equation, and breakfast is at least 50% of that. You start the day right and it will make all your goals easier to obtain.
I picked a healthy meal that I would eat everyday, no exceptions. It happened to be an egg sandwich with turkey. That sounds like it would be a problem, what with the protein/fat/carb combo, but if you're going to do it, do it for breakfast, and it's a helluva lot better than Cocoa Puffs. With this meal I take fish oil and calcium. You can take whatever you want, as long as you take fish oil. I recommend Flameout from Biotest.
After you become consistent with your breakfast, you can add in other healthy things, like lifting, cardio, and sprints. If you ever "fall off the wagon" it is because you added too much too soon. Don't despair, just back off the last thing you added and keep consistent with what you've been doing.
Keep following these guidelines and eventually everything will fall into place. Pizza will stop looking so good, soda will sicken you; things that once made you salivate will no longer have an effect.
While I've been fat my entire life, I am very experienced in fitness. I'm what you'd call an expert in failure. For years I started too big, failed, rinsed and repeated. It wasn't until last month that I finally figured out what I'd been doing wrong. I started too big. Small and consistent is greater than big and inconsistent.
One more thing that helped me immensely:
The Perfect Rep
Just type that in the search bar. If you feel drained during/after your workout, you're doing it wrong. Tired is one thing, but you need to feel powerful. You need to feel good. Who wants to workout if it just leaves them feeling broken? Following the advise in that article will give you the tools you need to become a beast in the weight room, and to leave it feeling like a beast, albeit a tired one.
Fitness isn't complex, hell, it isn't even hard. You just have to take the right approach. Start small and be consistent.