This problem can be solved by increasing the light intensity due to diffraction on the screen. It can be increased by using a wider slit that lets more light pass through. Increasing the distance between light source and slit will result in a decrease in intensity on the screen likewise increasing the distance between slit and screen.
Also, when slit width, $b$, is increased, the ratio $\frac{λ}{b}$ decreases, so for each wavelength, the central maximum will have smaller width, making it easier to locate distinctly.
