The right steps to follow
What I suggest is changing your eating and lifestyle so that you dont have an off season as such. Rather you allow your body to gain weight as lean muscle mass at a slow and steady pace without getting fat. There is no need for drastic changes and crash diets that as soon as you come off you gain all the fat back and end up looking out of shape. Look lean and hard all year round.
How best to do this
Number 1 thing is cardio! Do this year round. As a starting point I would suggest doing 4 x 35 minute sessions before breakfast. Do this for around 4 weeks to set a baseline to work from. I often get clients to perform much more than this even when not competing and always get them to use DNA Lean Thermo-XY fat burners for men prior to their cardio with 300-500ml of pure water. This significantly enhances fat burning by providing your body with key ingredients which actually help break down and shuttle stored bodyfat directly into your muscle cell's mitochondria to be burned as energy while you are working out. Number 2 - Eat the right type and ratio of macros. You should now be asking the question, what are the right types of foods, and what are the right amounts?
Choose the right foods
Have a balanced diet incorporating foods from all groups. Stay clear of refined sugars, excess salt and saturated and trans fats. For your protein sources ensure that each meal has a first class protein source coming from, fish, egg whites, poultry, red meats and protein powders. Carbohydrates should all be low GI a good selection to chose from but not limited to would be, Oats, Wholegrain rice, sweet potato, Yam, Bananas and apples. For your fats I would include all off these, Flax seed oil, almonds, walnuts, pumpkin seeds, soy beans and olives too.
The right amount of each macronutrient
This is not a figure that i can absolutely state. No scientist or lab is yet able to look inside your body and tell you how many grams of this or that your body is using or your requirements. The best way to do this is create a sensible baseline plan to work form. Base this on something around a 35% protein/40% carbs/25% fat/ calorie split. Start off with your protein intake. I would calculate this using around 1.5 grams of protein per pound of lean mass. For example if you weigh 210 lbs at 20% bodyfat that would mean your lean mass is around 168 lbs. Based on 1.5 grams of protein per pound of mean mass that would equate to 252 grams of protein per day. Since protein has 4 calories per gram, 252 grams of protein would give you 1008 calories. Now you have this figure you can calculate the other values based on this. Once you have your baseline plan in place, stick to it 24/7 for 3 weeks or so then you will have some idea of what if anything needs adjusting. If you do need to adjust, change only 1 macro at a time then work from there. Additionaly I would drink between 4 and 6 litres of water daily which will help aid in digestion of proteins, keep you hydrated and help keep you lean.
Pay close atttention to your meal timings and spacings. I would suggest eating every 3 hours. On training days I would eat 1-1.5 hours prior to your workout. Doing this will ensure your food has been sufficiently digested as to not have a totaly full stomach before working out. Since your food will be part digested it also be able to supply you with enough energy to fuel your workout. Post workout I would recommend using a mixture of whey protein isolate and either maltodextrin or vitargo for your carbohydrates - all mixed in water. If you eat 1.5 hours prior to your workout, lets say 30 minutes travel time to the gym, 1 hour working out, then have your post workout shake. This will fit perfectly with your 3 hour eating window. If your times vary a little then just adjust to suit accordingly. Depending on what time of day your workout I would suggest eating a minimum of 2 meals prior to your workout, 3 would be better, although I personally eat 4. This allows for enough consumption of proteins and carbohydrates to shift your body into an anobolic environment while working out. Although I have touched on what foods, how much and meal timings, I appreciate that putting a menu together isn't that easy - especially with variety! Therfore I can point you in the right direction for some healthy menu options to give you a few ideas when planning your nutritinal menu plan.
If you follow these basic steps to devise your own tailored nutritional plan, suited to your schedule and lifestyle, and ACTUALLY live by it, you will stay lean and muscular year round.
Good luck and all the best,