In order of importance:

1. get your nutrition in order
2. get your nutrition in order
3. resistance train (3 sessions per week, minimum)
4. cardio (2-3 HIIT sessions per week, 1-2 sessions of longer, more moderate cardio considered optional)

Nutrition, nutrition, nutrition. High protein, low processed carbs, lots of vegetables and fruit, minimize your sugar intake. Consider tracking your food intake just to make sure you're taking in what you should be. No juice, no soda, just water. No "low-fat" diet crap. Read labels. Learn the names of different sweeteners. Spoiler alert: they're in EVERYTHING. Don't crash diet or do any of that crap. Learn to eat healthy as a lifetime habit. Period. Whole, real, unprocessed food.

Muscle is metabolically active tissue, you want to retain what you have and build more with heavy strength training. Skip the crunches, they're not going to do jack for you. You need exercises utilizing large muscle groups and multiple joints - squats, deadlifts, chest press, pushups, pull ups. Train the core with planks.

Make sure you're focused on fat loss, not weight loss. Fat loss preserves muscle mass,while dropping the fat, weight loss is indiscriminate. For example, high doses of low intensity cardio will burn muscle stores along with fat, and you don't want this. Lots of overweight people finish marathons. Expert marathoners are thin, yes, but also have very little muscle mass. So don't run more, run smarter - with sprint intervals.

Oh, and sleep and get your stress under control. Tiny details.

You can tweak details like nutrient timing and stuff like that, but you need the foundations in order first. And skip on the "eat 5-6 meals per day". That's generally agreed to be old and inaccurate information. At the end of the day, it's the number of calories in, not when.