If you are meditating properly, you will get spontaneous inner joy. Nobody has given you good news, nobody has brought you any gifts, nobody has appreciated or admired you, nobody has done anything for you, but you will have an inner feeling of delight. If this happens, then you know that you are meditating properly.
There is also another way that you can know. If you are actually entering into a higher plane, you will feel that your body is becoming very light. Although you don't have wings, you will almost feel that you can fly. In fact, when you have reached a very high world, you will actually see a bird inside you that can easily fly just as real birds do.
If you have a good feeling for the world, if you see the world in a loving way in spite of its teeming imperfections, then you will know that your meditation was good. And if you have a dynamic feeling right after meditation, if you feel that you have come into the world to do something and become something - to grow into God's very image and become His dedicated instrument - this indicates that you have had a good meditation. But the easiest way to know if you have had a good meditation is to feel whether peace, light, love and delight have come to the fore from within.