Not to be forgotten, but sometimes overlooked inadvertently is the base of the fitness pyramid. Nutrition. So many times when getting started on some new fitness goals we focus
purely on the exercise portion and not nutrition. Whether your goal is to get leaner, or build muscle, adjust your diet first. The fuel you provide your body has a greater effect than a few extra reps in the gym or an extra 30 minutes of cardio.
Remember the base of "meats and vegetables, nuts and seeds, some fruit, little starch and no sugar". Also, "eat real food, mostly plants, and not too much". Remember too that fad diets don't give lasting results. There's a reason why every summer has a new one. The only real thing that works is eating real food in regular portions and eliminating processed, factory produced garbage. Real food grows in the earth, or once had a face, period. Stick with that and you'll be good. Then, based on your specific goals you can adjust the intake levels of proteins, fats and carbs. It's really not too hard to figure out.