First, you need to decide what your destination of choice is because different destinations use different default style templates:
1) ODS HTML -- uses a style template called 'DEFAULT' as the basis for all style attributes
2) ODS RTF -- uses a style template called 'RTF' as the basis for all style attributes
3) ODS PDF -- uses a style template called 'PRINTER' as the basis for all style attributes
4) in addition, for HTML-based destinations (HTML, HTML3, MSOFFICE2K) you can specify a Cascading Style Sheet for setting style attributes -- as an alternative to using a SAS Style template.
Second -- once you decide on your destination, decide WHAT style attributes you want to change. Then experiment with the existing style templates and see whether one is closer to the kind of output you want to generate. For example....for RTF destinations or PDF destinations... many people find a style template called JOURNAL is very close to what they want to generate (no interior table lines -- horizontal lines at the top and bottom of the table.
Third -- study an existing style template and learn about PROC TEMPLATE syntax and the ODS PATH statement. Search the Tech Support notes for examples of style templates for your destination. For example -- a style template designed for HTML (relative font sizes) may not work well with PDF which expects absolute PT sizes.
Last but not least, consider contacting Tech Support for help with style templates. There are many great Tech Support sites and FAQ available on PROC TEMPLATE -- but the steps to building a style template are lengthy, too lengthy to post all the steps here.