When writing a concrete poem, you must take into consideration the subject of the poem. Lets’ say the poem was about a tree. You might start by having the first line simply ‘A’, the second line might be ‘tree’, and the third line could be ‘is green’, and so on, with each line a little longer than the one above it. If you centered the poem, the finished product would resemble the shape of a tree. Now, that is concrete!