Good rule is moderation - if you were a big eater, do what nutritionists have recommended for years; your dietary needs include fresh fruits and vegetables (generally the darker the fruit or veggie, the more nutritional value it has - example: dark green vegetables as opposed to cauliflower and dark grapes as opposed to green grapes, etc...), you do need some protein, just don't over do it. If you like to have a steak, eat them once in a while and make certain you eat a cut that is less marbled or trim fat from the meat. Another good rule with meats and such have to do with portioning - nothing bigger than a deck of cards - this will assure you're not over eating. You're better to eat several small meals each day rather than a couple of large ones.
Watching sodium intake is important for many reasons - try to limit your intake and use alternatives such as sea salt or spices. It's amazing how you can find substitutes (fresh lemon juice on veggies instead of salt for example) and really don't miss the salt.
Intake of fiber is important - look for foods that are not heavily processed (additives, flavorings, preservatives, etc...) - for example; if you like pancakes - find a whole wheat batter - find breads that are whole grain and lightly processed or make your own; be smart about cereals - watch added sugars, trans fats and make certain they are whole grain.
Exercise is REALLY important. You don't need to over do it, but some exercise each day is very helpful. Many of us walk, interval train, run, play sports. You'll be amazed how conscious healthy choices in your lifestyle (eating, exercise, rest, activities, listening to your body and seeking regular medical exams, vitamins, etc...) come easier and easier - that's why many believe that post-donation can be some of the healthiest times of your life.
Enjoy and stay healthy my friend.
Scott