A tester should have a strong "test-to-break" attitude. 
He/She should be able to get complete picture of the system 
being developed. He should be able to think intuitively of  
actions to be performed to break the system(should be 
creative in breaking the system).

communication skills, Knowledge of testing types, ability to
analyze requirements, documentation skill, leadership quality,
analytical and judging skill

In addition to the above, the tester should not develop any 
hostility with the development team but only help them 
identifying the bug/error/defect in other words he/she 
should do the job perfectly. The tester should render 
his/her services.

tester should think like  customer 
then he will get bugs tester are the first customers to the 
product   so feel like customer and test the project

A good test engineer has a 'test to break' attitude.
An ability to take the point of view of the customer
A strong desire for quality, and an attention to detail.
Tact and diplomacy for maintaining a cooperative 
relationship with developers.
Testers are fundamentally honest and incorruptible 
Last but not the least is “Patience

A good test engineer has a 'distructive' attitude, an 
ability to take the point of view of the customer, a strong 
desire for quality, and an attention to detail. Tact and 
diplomacy are useful in maintaining a cooperative 
relationship with developers, and an ability to communicate 
with both technical (developers) and non-technical 
(customers, management) people is useful. Previous software 
development experience can be helpful as it provides a 
deeper understanding of the software development process, 
gives the tester an appreciation for the developers' point 
of view, and reduce the learning curve in automated test 
tool programming. Judgement skills are needed to assess 
high-risk areas of an application on which to focus testing 
efforts when time is limited.