The best time to start was 6 months ago. The second best time to start is today.

6 months ago I graduated from veterinary medical school and came to a sobering realization: after 11 years of busting my ass to improve myself from the neck up and follow my dream, I was profoundly unhappy with the person that I saw looking back at me in the mirror. After doing some research on reddit and elsewhere I decided to start a journey to make my outer appearance a better reflection of who I felt my inner self was. Here's what I figured out along the way that I wanted to share and hopefully help others make the same journey.

Fitness:
1) Three acronyms cover 90% of what you need to know here as a beginner: PPL, CICO, and HIIT. My workout plan involved PPL 6 days per week and HIIT cardio on my “off” day, and my CICO calculated out for weight maintenance.
2) Don't neglect your shoulders, chest, and back. These are the muscles that control your posture, and posture is a major factor in the first impression that you make! My posture for most of my life has been, for a lack of a better word, absolute shit. Weight lifting was able to dramatically change that in just 6 months. Shoulder shrugs, bent over rows, flat bench press, incline bench press, overhead press, and push-ups are some simple exercises to make sure are in your routine if you're looking to improve your posture.
3) Nutrition, nutrition, nutrition. Set macro goals that match the look you're aiming for. If you want to gain muscle, or maintain muscle in the face of weight loss you're going to want at least 0.75 to 1 gram of protein per day in your diet for each pound of lean body weight. Avoid simple sugars like they're poison. Don't drink your calories (unless they're helping your macro goals, like protein shakes). If you're eating a high quality diet you shouldn't feel hungry between meals even if you're in CICO deficit. If you're wasting your calories on shitty food, that's how you end up counting the hours until the next meal.

Time management:
1) If there's one thing that four years of 60-100 hour work weeks in veterinary medical school taught me, it's that there's a shit-ton of hours in the week to get things done and still have time left over for fun as long as you're managing your time well. Most people don't have a “too busy” problem, they have an efficiency problem.
2) Manage your sleep: too much or too little is bad. I shoot for 6-8 hours per night. Sleeping more than you need wastes hours and leaves you feeling more sluggish and tired than you would be on regular sleep. Sleeping too little leaves you exhausted and unable to make the most of the hours that you're awake, and undermines the work that you're doing on your fitness. Wake up at a normal “work” time on your days off – keeping a steady sleep schedule will help you stay more rested and those morning hours on the weekend are a great time to get shit done so that you can enjoy the rest of the weekend guilt-free.
3) Trim your priorities. Most people respond to feeling unhappy about their lives by trying to add things to it. This is the opposite of what you should be doing. Having fewer, more meaningful commitments will leave you happier than having many, less meaningful commitments all competing for your finite free time. Identify the people, hobbies, and things that make you happiest and direct more of your time and energy in those directions. Simple is happy.
4) Have a schedule for the day, even if you don't have anywhere to be. Splitting your time up into “work” and “play” blocks helps keep those lines from blurring. That means you get more during your work time, and enjoy your play time more because you don't have the guilt of neglecting your work since it has its own time set aside.

Outer appearance:
1) Basic men's fashion is pretty damn easy if you're willing to add an extra 10 minutes to your day. A button down shirt, a pair of slacks, a belt, and some basic dress shoes will make you look pretty sharp as long as you buy clothes that fit and/or get your clothes adjusted so that they do fit. Make sure your pants fit at the waist and hips, you can always get the length hemmed.
2) Treat yourself to a haircut that isn't a $15 Supercuts hack job. This is one of the centerpieces of your outer appearance. Your hair makes a statement about how you want to present yourself. Don't make that statement “I spent more on the delivery pizza I ordered last night than I did on this haircut”.
3) Grooming and hygiene: This one explains itself. No matter how well you dress or how much work you do in the gym/kitchen, if you smell bad or otherwise aren't keeping up with your grooming and hygiene you've completely undone all your work. Brush and floss your teeth. Shower every day. Shave or keep your facial hair groomed.
4) Do not underestimate how much of your outer appearance is within your control. The fraction of people who are truly so physically unattractive that they can't make meaningful improvements to their outer appearance is extremely small. Don't fall victim to apathy because you underestimated what your ceiling was. Put the work in to try and find the best possible version of yourself. You'll probably be pleasantly surprised at what you find.

My progress so far after 6 months.