Here are the design steps to be followed for an unreinforced masonry wall.

1. Estimate the self weight and imposed loads. See IS 875 part 1&2 on how to go about it.
2. Estimate the eccentricity ratio taking moments about the centerline of the wall. You can use the equation stated below to calculate eccentricity ratio. WE=w1e1+w2e2 where W is the weight of the masonry wall and E is the eccentricity. Eccentricity ratio is E divided by thickness of the wall.
3. Estimate the effective height, length and thickness of the wall.
4. Calculate slenderness ratio as the lesser of the 2; effective height / effective thickness or effective length / effective thickness.
5. With the eccentricity and slenderness ratios; estimate the stress reduction factor from the code . If necessary you can also estimate area reduction factor and shape modification factor.
6. Calculate the compressive stress of the wall based on the wall load. Then divide by stress reduction factor, to arrive at the basic compressive stress required.
7. Apply increase in  basic compressive stress if eccentricity is significant. Increase of up to 25% is allowed by the code
8. With the help of TABLE 8 of the IS code 1905,and using the basic compressive stress, chose the appropriate unit strength and mortar mix required.