[CentOS] Very slow disk I/O

Hi Users

I am using RHEL 6.5 on my server.

 From top command i can see that the processors in my server are 
spending a lot of time on wait for I/O.
I can see high percentage in terms of 30-50% on "wa" time.

Here is the df output about the disk space in my system:

**********
[root at localhost images]# df
Filesystem      1K-blocks      Used  Available Use% Mounted on
/dev/sda1      1915071844 103227908 1714563936   6% /
tmpfs            32931472         0   32931472   0% /dev/shm
**********

Could someone point me on how to improve the disk I/O on my server and 
reduce the wait time on I/O.

Thanks
Jatin