Just eat good stuff -- whole, fresh vegetables and lots of them; high quality naturally raised meat if you can get it, fruits in limited amounts (preferring berries to large fruits like apples & oranges), and drastically reduce foods high in carbohydrates (anything made with grain, anything made with sugar). And keep your portions reasonable.
I recommend completely eliminating all sweetened drinks (including those using artificial sweeteners) from your diet. Get used to drinking unsweetened beverages -- water, coffee, tea, milk if your stomach can handle it. But mostly water.
You should also go through your cupboards & fridge and get rid of all the junk -- chips, crackers, cookies, desserts of all kinds, candy, etc. Just remove it from temptation.
The nutrition plans for Beachbody workouts vary, but they all emphasize whole, healthy foods. There's a lot of variety and a lot of great food to eat. You won't be starved and you won't get bored. The only reason people say things like "just eat grilled chicken and brown rice" is because it's brain-dead simple. You don't need to be that boring.