I would start with sleep - it sets the tone for your day and your mood. If you are well-rested, it makes eating healthier and getting exercise easier! So I would start there.
Then, I would focus on eating well. You eat 3+ times per day, and making even small improvements to those meals can ultimately have a huge effect.
With your sleep and nutrition in line, make time for exericse. Even if it's a 10 minute walk at work or busting out a few push-ups as soon as you get out of bed, you can start to add more movement in to your day!
Last - I'll say that working with a coach can really help you get these things in line faster and with less stress. We can work together so figure out how you can get more sleep in your busy day, how you can add nutritious foods without a lot of extra cost or time, and simple tricks to get more exercise into your day. I'd love to work with you!