Easy - carbs in morning and around workout. Otherwise, mostly protein and healthy fats (olive oil, nuts, fish etc.) with plenty of veggies.
Good carb sources are white rice, potatoes, sweet potatoes, berries, bananas, apples, oatmeal (if you don't have an adverse reaction to it).
As for the glycemic index - while it has merit, if you're eating a good amount of protein and fats with the carbs, the insuling spiking effect of high glycemic index foods is drastically lowered.
In the morning I like to eat berries in greek yogurt, an apple or banana, 3-4 eggs and sometimes a couple strips of bacon (I love the stuff). Your body responds well to carbs in the morning, so this is the time to have them. Oatmeal is a go.
Pre-workout I like to have a whey + glucose shake.
After workout, a solid meal with rice or potatoes, chicken or beef, and a good amount of veggies.
Apart from that, lots of protein + healthy fats + veggies.
Carbs are ONLY used as fuel. They have no other purpose in the body. If you don't use them, they get stored as fat. Carbs also happen to be really easy to consume in mass amounts compared to protein and good fats (you get full faster from the last 2). Thus, limiting carbs tends to limit bodyfat formation. A good amount of carbs to aim for is 100-200 grams per day.
The amount of carbs you can to eat depends on how well you handle them - some people get fat just by looking at them. Others can shovel away plates of pasta and never gain an ounce of fat. Determine which kind you are (or somehwere in the middle) and adjust your diet accordingly.