1. DO IT FOR YOU. I swear this is cheesy but it's true, and hell, it's true about a lot of things in life when you really think about it. You have to do this for yourself, not for a "summer body," or a significant other, or any other silly reason. It seriously has to be for you, otherwise it will fail, I promise.
2. DO IT THE HEALTHY WAY OR NOT AT ALL. I've had a lot of friends who've gone to the gym with me and started the journey with me, and I've seen a lot of them get out of hand with how obsessive they are with their work out/eating plans. If at any point you think, man, I would be worried about someone if I saw them doing this to themselves, THAT'S A HUGE RED FLAG.
3. This goes hand in hand with the above tip, LISTEN TO YOUR FRIENDS AND FAMILY. I don't mean this in the sense that they're always going to be right about you and what you're up to with your life. But if someone comments on something you're doing that they think might not be quite right, listen to them. This is the toughest one, I know from personal experience, because for a while I was losing weight in a very unhealthy way. And anytime someone commented on it, I became extremely defensive.
4. DRINK A SHIT STORM AMOUNT OF WATER. I think a lot of people don't understand how important water is... it is literally the only beverage you need. If you cut out all the other beverages you drink, and only had water, you'd lose at least 25 pounds in a month. Now, I'm not saying I'm perfect, I still have an occasional drink when I'm out with friends. But, what I'm saying is water should be your primary resource. It really gives off a big difference.
5. FIND A PLAN AND WORK HARD. For me, what's worked well is the fact that my whole family is on board now, even my little sister who doesn't need to lose weight. But, she's on board in a sense that she doesn't constantly ask for junk food when we go out to the grocery store. I'd say if you can't get your family on board, find a friend! And hey, there's no shame in not being able to find a friend either, so try out online message boards for fitness. I personally use myfitnesspal, it kicks ass.
These are pretty simple tips but they're things that took me two times to learn right, so I figured this post might help some people out there. :)