I have used excel commercially for a number of years, and find that the best solution is to trust your own styling.
The best way to maximise your potential in this area is to play with the properties & formats dialogs for everything. That is, all components of any chart you create, and when you right-click a selection of cells and choose "format cells" you should get to know every detail of the options available and play with them until you become hooked.
Lots of use of subtle colours (use shades rather than colours), and dotted & thin borders, frozen panes, hide gridlines, etc etc...
Keep the worksheet tidy and hide anything not required by the end user (eg. extra sheets not in use)...
Hope this helps and is not patronising, i find that the more you play the more intuitive your own talent becomes.