You don't have to stay ripped year around, but you absolutely can stay lean and pack on quality muscle by doing the following:

1. Shoot for 1 to 1.25 grams of protein per pound of bodyweight. Don't piss me off by asking if that's "grams per pound of lean body mass." No. It's grams per pound of bodyweight.
2. It's unlikely that protein can be turned into fat, and there's never been a single study done that shows that very high protein diets cause any health problems. So, when in doubt, eat more protein.
3. Include most of your daily carb intake in your peri and post-workout feedings. This is when your body will be able to use the incoming nutrients most efficiently for replenishing glycogen and uptake of amino acids into the muscle. It's also when it's less likely to store it as body fat.
4. Get your fat sources from nut butters, nuts, olive oil, and fish. But don't go crazy here. Watch those calories.
5. Eat two pounds of vegetables a day, minimum. I don't need science for this. Just do it and thank me. Veggies will improve your digestion and fulfill your micronutrient needs. Get a lot of different "colors" in there to ensure your bases are covered.
6. Do your best to eliminate processed and fast foods, candy, and soda from your diet. Having them in moderation is fine, but try to meet the 90% rule (eat right 90% of the time) in regards to eating quality protein, good fats, tons of vegetables, and pushing your carbs into peri and post-workout meals. This really uncomplicates things.
7. If you need to gain more weight, eat more carbs during your post-workout meals.

Yes, it really can be that simple.