How to draw the inverse of a function ?

There is a simple trick to drawing the inverse of a given function. 

First, roughly sketch the original function. This means a sketch of the general shape of the curve with some key characteristics such as its turning points, y-intercept/s , x-intercept/s etc.   

Also, usually when you are asked to sketch a graph, you will be given limits so make sure you sketch up to the appropriate limits. If you are not given limits, use your judgement to pick suitable boundaries that allow you to get the gist of the shape of the graph. 

Then, reflect your original graph in the line 'y = x'. This gives you the shape of the inverse of your function.