Parameter need to Change for Performance Tuning

Below setting can Improve overall performance of whole DB's

Default values 

optimizer_index_cost_adj=100  --> Low value means index scan is less costly (Low value force index use)
optimizer_index_caching=0     --> High cache means more chance for nested loop first in below loop style

• Nested loop joins
• Hash join access
• Full-index scans
• Full-table scan access 

I have a query that performs bad (did not return after more than one minute). 
After I issued the following if worked well.
alter session set optimizer_index_cost_adj=5
alter session set optimizer_index_caching=90

Can use hint in sql statement.

select /*+ opt_param('optimizer_mode','first_rows_10') */ col1, col2 . . . 

select /*+ opt_param('optimizer_index_cost_adj',20) */ col1, col2 . .