There are three main rules to maximizing the healthy food and minimizing the sugars and other carbs at a fast food restaurant:
1. Compare the Nutritional Information at the fast-food restaurants in your area. Below are links to the nutritional information at most of the popular fast-food chains. In particular, look for salad dressings with little sugar -- some have packets with over 4 teaspoons of sugar included! And look for other low-carb items such as these:
2. Order Salads with Grilled Chicken (not "crispy fried", or other chicken with breading). Occasionally, you'll see salads with other protein, but chicken is the mainstay of fast-food meal salads. Tips: 1. Skip the croutons, tortilla strips, and similar additions. 2. Be very careful about the dressing! (This cannot be over-emphasized. You may have to bring your own.) Also, look for salads with a mixture of greens, and a variety of vegetables.
3. Order Burgers and Sandwiches Without Bread - Again, check the carb counts ahead of time. Anything breaded and fried, as most fish and many chicken sandwiches contain, is going to have a lot of added carbohydrate. Add a "side salad," following the above tips, to the bunless sandwich. In some places, you can ask for a separate larger container such as those the meal salads come in. Then dump the side salad into it, and put the protein on top.