1. Dress the part
Having the right equipment for whatever you're doing is always important, and clothing counts, too. You won't have any desire to exercise if the clothes you're wearing are restrictive or uncomfortable. Performance gear can get expensive fast, but a few basics needn't break the bank. You'll be much more comfortable in a moisture-wicking shirt than in an oversized cotton T-shirt.
Now, I fully admit that I have more than a few insecurities about my body, and wrapping myself in spandex does nothing to allay them. As a result, I usually take a few extra steps to make sure that my workout wardrobe inspires me as much as my vintage one does. If you feel similarly, it's well worth the extra time to find clothes that you like (I color coordinate my workout gear) and a sports bra that flatters and doesn't just flatten.
2. Do what you love
Willpower is an expendable resource, and if you don't like what you're doing it'll be much harder to make a habit of it. Don't like going to the gym? Try something else. Don't like exercising alone? Find a buddy or take a class. I enjoy being outside, so running, hiking, and biking are some of my favorite things to do. On the other hand, I took a yoga class and just couldn't get myself to practice regularly at home, so instead of feeling guilty for failing, I put it down as Not For Me and used that energy for more valuable things.
3. Keep count
Calorie counting isn't for everyone. But if you've never considered how much you eat in a day and feel like you have no idea what "one serving" of anything is, it can be a very valuable tool. A lot of packaged foods these days are marketed as being 100 calories per serving, but often the serving sizes are small or awkward in an attempt to convince the weight-conscious consumer that the food is a healthy option. I count calories on MyFitnessPal (drop me a line if you want me to add you as a friend!) which allows me to budget my consumption a little more mindfully. Once you get into a routine, the foods you eat regularly appear at the top of the list for easier access, and with a little practice you'll get better at eyeballing things without measuring or weighing. Don't drop your calorie consumption too low (I aim for a 250-500 calorie deficit a day) and don't expect anything to change overnight.
It's hard to maintain healthy habits in the long run, especially if you feel like you're depriving yourself. Since long-term changes are more likely to succeed than fad diets or other short-term solutions, it's important to feel like your food changes are sustainable. For me, this means figuring out what desserts I can have that satisfy my sweet tooth without blowing half a day's calories, and eating them regularly. Ice creams, sorbets, and sweet coffee drinks usually fill this niche for me, and I've doctored a mug brownie recipe down to a personally acceptable amount of calories as well. I also make a point of having a few "luxury" meal options to eat during the week, which are all over the spectrum as far as calories are concerned. Fish, shrimp, and avocados are some of my favorite healthy indulgences, and incorporating them into my diet from time to time helps me feel like my dining is gourmet rather than spartan.
5. It's OK to say "No"
As a kid, junk foods and sweets were pretty scarce at my house. As a result, any time I was presented with a buffet, I snarfed treats and chips like I'd never see them again. Even now, it's a challenge to walk into the fellowship hall after a church service and not walk out with a plate loaded with tiny cupcakes and store-bought cookies. It's important to remember that you don't have to eat things just because they're free or just because they're sitting there. Try one and savor it, and let other people eat the rest. If it isn't something that you love, turn it down politely. I'm trying to make sure that I don't eat food just because it's free (the college student in me always wants to) by making a personal rule that I'll only have one of something, and even then only if it's homemade or my very favorite thing. I wouldn't eat a Chips Ahoy cookie or a pile of Oreos normally, and there's no reason to eat them just because they're sitting out on a table.
And, one last one: Don't expect anything to change overnight. Give yourself a month. Two months. Be patient with yourself!