"If I can just fit back into Y, I'll be fine"
That is the exact WRONG way to go about your weight loss. All above the above are hopes. Wishes. Desires. And none does a thinner body make.
What you need are detailed, definite goals that are written and time bound (e.g. "over the next 3 months") to hold yourself accountable to doing what you said you were going to do by the time you said you were going to do it.
Adopt a step-by-step course of action to get you there
In order for this to work there needs to be a concrete method to your weight loss madness. To this end, you need to chose a weight loss plan that will lead you step-by-step through what to eat (and what not to eat), how and when to exercise, and every other imaginable aspect of losing weight. The reason for this is that goals have a much better chance of becoming reality when they are being attained as a result of a plan or system of action.
Get started IMMEDIATELY
Most flunkies know how to study. Most broke people know how wealth is generated. Most overweight people how to lose weight. However, what separates all of these very knowledgeable, yet unsuccessful people from the results they desire is action. Don't let that be your fate.
Once you have written specific goals and chosen a plan of action, don't delay in getting right on track to weight loss. The cheesecake, burgers, chocolate, and pastries aren't going anywhere. You can snack on them moderately once you've achieved your goals. Don't get caught into the trap of holding off having Your Best Body any longer. The sooner you start, the sooner you'll be done.
Be Prepared for the emotional roller coaster
Nearly everyone who has tried to lose weight has had some level of success at one time or another. For those who have not been able to sustain desirable results, being knocked out by the emotional roller coaster is most likely to blame.
Look, losing weight is very simple, but not easy. If it were, there wouldn't be so many people trying to get it right. The #1 skill that you will need to develop in order to make it through is surviving the roller coaster of emotions. One day you'll feel as if you're getting great results. A week later, you may actually feel that you are moving backwards. Either way, just know that as long as you consistently follow the weight loss principles, you will ALWAYS move forward, even if it does not feel like it.
Don't stop until your goal is reached, no matter WHAT
So many times people come to a screeching halt in their efforts to lose weight and diet because they get discouraged a portion of the way through OR after they reach a certain benchmark they allow themselves to be satisfied and quit the program even though their goal has not been reached.
DON'T DO IT.
There was a specific reason that you set your initial goal. Do not sell yourself short by settling for anything less. Stick it out until the very end, and your sense of accomplishment will be irreplaceable.
Once you've reached your goal, never, EVER let yourself blow up
This is the last and final barrier to ultimate success in your efforts to lose weight.
Make sure not to allow yourself to relapse while you are in maintenance mode. I recommend sticking to the same general principles that helped you lose the weight and then occasionally indulging in some of the foods that you love. This balance is the best way to keep the body that you've worked for and not feel over-restricted.