How to Get Your Act Together

The Preparation Advantage
Chefs do this thing called mise-en-place, which is French for "everything in its place."
The purpose is not just to make sure you have all the ingredients, but to make sure you're organized and ready to cook, and in turn, it makes the actual cooking part a breeze. 
Mise-en-place is about doing all the little things up front in order for the most important things to happen without a hitch. 
Everything that can be assembled ahead of time is. Veggies get chopped, meat gets thawed and seasoned, stuff gets measured, or at least brought out so that it's accounted for. Then as mealtime approaches, it'll only take a bit of effort to cook.
Mise-en-place gets your mind focused, deletes distraction, and simplifies cooking so that you, as a chef, can go from having to consider many components to just a few.
The Missing Link
Think about those who struggle with getting in shape. It's usually not that they're ignorant about choosing better food or getting off their couches, it's that they're disorganized, distracted, and complicating the process.
Their lifestyle mise-en-place is mucked up. Their meals are haphazard -- flipping between inadequate and excessive. Their workouts are hit or miss. And they usually lack structure, direction, or preparation. 
When nothing is in its place, everything seems like a good excuse to stop eating well and training hard. 
I'm not talking about household or environmental tidiness, although those too can have an impact on your mental clarity and discipline. What I'm talking about is a lack of planning, a lack of preparing for setbacks, and a lack of doing all the little things up front to make the important things happen without a hitch.
Lifestyle mise-en-place eliminates the excuses before they arise. You cook the food ahead of time. You have the healthy stuff ready to go. Potatoes, check. Chicken, check. Veggies, check. Slow cooker stuff, check. And whatever healthy foods work for you personally, check.
Mise-en-place also means you've got what you need to work out. You've carved out the time. Your clothes are laid out. And you've got a plan so that there's no hemming and hawing or flaking out on the last second. You know exactly what to do.
It's making a commitment through your habits, so that the hard stuff is easier to pull off. 
Mental Preparation
Let's expand mise-en-place. Because being fit includes mental preparation too. 
Have you thought about what you're going to do when your diet feels like it's too hard to stick with? Have you considered what actions you're going to take after you've slipped up with either your eating or your workouts? More importantly, have you considered what might cause you to slip up in the first place?
Get those three questions straightened out and you'll master your fitness. Let me help... 
1. When your diet feels like it's too hard:
You start eating in a way that seems healthy and disciplined. You feel like you're "behaving" yourself. And at first you're proud of making such changes, but over time it gets harder and all you want to do is eat everything you gave up, with abandon. 
You're tempted to go back to your default eating patterns, the ones that feel comfortable -- but also the ones that make you feel shackled to a lifestyle you hate and a body you're not proud of. 
Mental mise-en-place:
Mentally prepare to avoid blaming yourself. That may be tempting to do, but it won't help.
Go back to the drawing board. The plan you're following is inadequate if it's making you constantly feel like you're on the verge of giving up. 
Consider the possibility that your energy expenditure is too high for the amount of calories you're taking in. Trying to under-eat and over-exercise in an attempt to lose a lot of weight isn't something you'll be able to sustain. Your cravings should be a red flag.
2. After you've slipped up:
You anchor your nutrition and your fitness together, so when one sinks the other goes down with it. You stop working out when you screw up your diet. Or you give up on trying to eat healthfully if you can't make it to the gym. 
Mental mise-en-place: 
Mentally prepare to move on. Mentally prepare to go to the gym at your worst. Even when you've overeaten. Even when you've taken some time off. Go when you're feeling fat or unmotivated. Tell yourself those feelings will pass. 
When you work out at your worst, it'll be that much easier to work out at all other times. It'll help you solidify the routine.
You can start slowly too. Write your workout down, tell yourself you'll just do the first exercise, and then see how you feel after that. Chances are, you'll end up doing the rest of it. 
When you're feeling shit, train simply for the pleasure of accomplishment. Because it's something you have complete control over, and it’s a guaranteed job well done that'll carryover into other things you do.
Likewise, if you feel like saying "screw it" with your diet just because you haven't been working out, change your thinking. 
Realize that when you eat well you'll have the energy to be more active, and you'll feel better about yourself in general. It's all the more important to take care of your nutrition when you're not working out.
3. When you can't seem to stay on track:
You keep trying to eat well and exercise consistently only to end up getting caught in a cycle of all-in or all-out.
You diet hard, you train hard, you suffer; then you fail miserably and feel unmotivated to try again.
Mental mise-en-place:
Mentally prepare to make smaller adjustments with your diet even when you're motivated to make big ones. Remind yourself of how those big "improvements" often lead to big setbacks. 
If your dieting patterns inevitably lead you to a place where you're tempted to shove the junkiest food you can find in your mouth, then you're not getting enough nourishment, or the right kinds of food at the appropriate times of day. 
I see this happen most often with people who pride themselves on being able to stave off hunger during the day. Sure, they may stave off hunger in the early part of the day, but then end up making up for it at night. 
Skipping a reasonable 400-calorie breakfast or lunch won't compensate for that 3000 calorie splurge you'll want as a result at night.
Likewise, when it comes to working out, your first step is consistency -- not becoming a superhero in your first workout. 
After a long period of inactivity, it's more important to have workouts that you can do consistently, instead of doing one really hard workout that leaves you incapacitated for several weeks until your next attempt at being a superhero.
The Effort is the Reward
Mise-en-place gives you the advantage on consistency.
You think ahead. You prepare for downfalls. You get your stuff organized. And you eliminate all the potential obstacles ahead of time -- both mental and physical.
When you've accounted for all those things, then you can savor not just the outcome of what you're doing, but the consistency of training hard and eating healthfully on a continual basis. The continual effort is also the reward.
Five Final Tips:
Tip #1. Know what your main goal is and have a plan to make it happen. Write and organize your workouts for that specific goal, or hire a trainer who can help you reach it. 
Tip #2. If you've never kept a food journal, do it. Don't worry about calculating anything. Just jot down what you eat at mealtimes and about how much. Notice how these things make you feel. Pay attention to the signals your body gives you.
Tip #3. Notice when you're reaching for food for the wrong reasons. If you can't control your anxiety, anger, sadness, or any emotion, realize that food won't fix it. It's bad as a band-aide.  Don't snack just because you're bored, or it's free, or because everyone else is snacking on the same nutritionally void shit. 
Tip #4. Eat meals on purpose. Then stop and wait till your next meal before eating. Don't skip them if you have a tendency to overeat later on. 
Tip #5. Keep a workout log no matter how advanced or inexperienced you think you are. This is essential if you weight train with a specific goal in mind. Write what you're going to do before you get to the gym. Then follow everything the log tells you to do. It makes you prepared, efficient, and focused -- which is what mise-en-place is all about.