Rectification error is one the difficult problems for students, I too find perplexed when I was in high school. Here is one example for how to handle error. This below example explain first type of rectification of error. 

A. Sum of Rs. 2500 paid by way of rent has been debited to landlord's personal account.

If you know the correct entry then it would be easy to rectify ( be master in Journal entry). Look at above example 

1. Just Ignore common name entry.

avoid same entry i.e. To Cash 

2. Maintain the correct entry as it is.

i.e. Rent a/c 2500

3. Wrong entry must be balanced by ' to be credited'

i.e. Landloard a/c 2500

4. Finally,

Rent a/c 2500

To Landlord a/c  2500.

(being error rectified )