This is a difficult question to answer, because you have posed it in a very general way.
As stated above, you want to minimize database hits, especially if the application needs to scale to many end users. You also want to make sure that your database queries execute as efficiently as possible, so the design of the tables and the indexing that is applied to those tables will be important.
You also want to avoid making the UI too complicated. Presenting too much information at once on the display takes longer to render and may also confuse the end user.
If you have specific concerns about your application, you may want to engage the Pega consulting services.