If portion control is part of your diet struggle, the best tool you have to judge whether there's too much food on your plate is one you already have with you: Your hand. This graphic shows you how to judge servings of meat, pasta, even butter with your hand and fingers.
The graphic below shows you what you need to know, but the gist is that if you draw a rectangle across the centre of your hand, long-ways across your palm, you should have roughly a 85g serving of meat or fish. Ball your hand into a fist, and draw a rectangle across the tops of your knuckles and you have the size of a half-cup of pasta. The tip of your finger, from last knuckle to tip, is about one serving of butter. Your thumb, from knuckle to tip, is roughly the size of a tablespoon, so you can use that to average all sorts of measurements.
Obviously, everyone's hands are different, and all of these are very rough measurements — an 85g serving of meat that's the width and length of your palm but is ridiculously tall obviously breaks the whole thing. Similarly, just because something is "one" serving doesn't mean that's all you should eat. The goal is to offer a guide to how much you put on your plate (since "serving" is a pretty vague term in and of itself) and to cut down on mindless eating. Hit expand to make the image below bigger, or hit the link below.