That is only possible when you will brainstorm for ideas; brainstorming is itself a long process which deals with the generation of different ideas. Take a pen and paper; just write whatever comes to your mind. The list will then be shortened; select the best one out of it, the basis of best one would be the one which interest you the most so that you don’t lose interest while writing at any stage. You can generate different ideas by looking around in your surroundings. For example; you can see there are boys and girls or men and women; you can compare them in your analogy essays.