Start with clue 11 which fixes the house of the engineer. From there, you can use clues 10, 12 and 20 to fix the houses for the stated characteristics. You can use clue 3 to fix the house of the lawyer.
After you have fixed the house of the engineer and the lawyer, you can use clue 13 to fix the house of the accountant and salesman.
The remaining two occupations are the technician and doctor. If you study the clues 2 and 8, you will be able to find their houses.
It will quite easy to complete the remaining clues. Look for the clues that fit exactly into the blank squares (i.e. only one solution).
If you take step by step, you can complete the whole quiz. It may take you 30 minutes to solve this quiz the first time, but with practice, you can reduce the time down to 10 minutes for a similar quiz.