For tuning of reports we can use the following ways
1 Check the option Perform grouping on Server, Use indexes 
or server for speeds. 
File>Report Option>Perform grouping on Server.
File>Report Option>Use indexes or server for speeds. 
2 Instead of joining DB tables on report , use add command 
option. Put all the filters, Prompts in SQL command. This 
way report will run faster.
3 Uncheck option save data with report.
File>Report Option>Save data with report.
4 If report contain Many Sub reports, use a prompt which 
ask whether you want that particular data or not. If Use 
chooses no, then that prompt’s data value should be in 
Report selection criteria of report. based on that value do 
coding to not to get data on report.
(With Best of my knowledge)