Mahadi Hasan Miraz I have never seen a worse graph than the one your linked to! The grid lines make the data almost invisible. You should have a look at the work of Edward Tufte, who coined two important terms : data ink and chartjunk. Data ink is the amount of 'ink' on the graph that shows data. In the case of the awful physics graph, the amount of data ink is close to zero. And further down the page, the author goes on to plaster equations all over the graph, burying the data even further – this is chartjunk.
If you cannot differentiate between the items, consider plotting groups of items that represent meaningful subgroups of the item pool.