Rules and targetting features / OSM sources / Maperitive

A new user to Maperitive and OSM,

I'm looking to render a map based on a custom ruleset, I understand how to create the ruleset based on tutorials from other blogs but do not appear to get results i expect so want to check i have this workflow / process correct.

Brief introduction: My understanding of the process required to render a map based on custom rules

1. Define approximate area of interest on maperative via geometry bounds
2. Create the ruleset; testing on a very simple one which pulls in roads and universities/hospitals only based on tags roads amenity *healthcare
3. Download OSM data, maperitive pulls in data for tags roads amenity *healthcare and renders them to colours widths defined:
4. Generate and render map; rendered map should be returned showing only items that have been tagged as road amenity healthcare

Is that understanding right, am new to code generally so feeling quite overwhelmed on the learning curve required just to create the ruleset! My end map would ideally have the city with all buildings/roads/features but universities picked out in a separate bright red colour based on my ruleset which has turned off all the other labels and colours to focus the map on just those facilities. All/any help really greatfully appreciated