Performance improvement with elastic search

Hello,

We are developing one application in which we are using Elastic Search as our data storage. We have setup Es with 5 shards and 1 replica. And while adding data into ES we are using routing of course for performance part. And our system has 8 GB of RAM. Still we are not getting the performance upto mark. Still anything we are missing as a part of setup in ES. Any settings we need to change in yaml file. As we are new to ES setup please suggest best way to use ES with optimal query output.