How to tune query in a large partition table

Hi,
I am having a partition table having a large size. I have to tune queries to fetch data from the table. The details are as follows:
1. Table is having 10 cr data in each partition and avg. rowsize is 167.
2. Currently there are 40 partitions and only 3 partitions are loaded with data.
3. Total no of columns in the table is : 52
4. The partition table I had creted as composite partition i.e partition is in the date field and in each partition is having 8 hash partitions.
5. The data is loaded in the table by SQL* Loader.

Actually I had created one local index in the partition table to fetch the data faster, but due to the index the loading was very slow , so I had to drop the index.

Can you please help me what is the best way that I can fetch data from the table easily?

Rebuild index after ETL.