Performance tuning is a very large subject - and much time spent looking through old JDEList posts will reveal a lot when it comes to tuning for performance. I believe I also have a whitepaper on my website that talks about performance tuning.
However, in summary -
1. Make sure your architecture is set up correctly - ie, don't use RAID5, place TEMPDB on a fast performing drive etc
2. Check the code in the application - 99% of the time performance issues is the result of an application not correctly using an index or not written correctly.
3. Run JDEDebug logs and push these through the Performance Workbench - available on the knowledge garden - to identify performance timing issues
4. Extract long-running SQL Queries and pass these through Microsoft SQL Index Tuning Wizard to identify issues
5. Re-write code if necessary to perform the job you want faster.
Hope that helps - again, these are the top high-level methods of tuning for performance - if you have a specific issue I'd be glad to try and help.
